Choosing temperature monitoring: paper log, data logger, Wi-Fi sensor or wireless with mobile connection.
Whether it is a fridge in a restaurant, a vaccine fridge in a practice, a cold room, a server room, a museum store or a freezer at home: temperature can be monitored in very different ways. This guide compares five types without naming brands. It shows what they typically do, where their limits are and what authorities in different sectors expect from measuring devices. Which requirements apply to you depends on your sector and country. The competent authority decides.
- Paper log: a deviation is only noticed at the next reading. A min/max thermometer shows the extremes, but not when or for how long.
- Data logger: records every value at the set interval. You typically only see the history when you read it out.
- Wi-Fi sensor: alerts you remotely as long as Wi-Fi, router and internet are running.
- Wireless with mobile connection: alerts you remotely without Wi-Fi on site, but needs mobile reception at the gateway.
- None of these types cools, and none measures the core temperature of a product unless a probe sits in the product or in a buffer.
- Authorities: depending on the sector, they expect for example daily checks, recording thermometers, alarms or calibration certificates.
Who this guide is for
- Restaurants, hotels, butchers and catering kitchens with fridges and freezers
- Pharmacies and medical practices with a medicine or vaccine fridge
- Logistics and warehouses with a cold room or freezer store
- Operators of server rooms and plant rooms
- Museums, archives and collections
- Private users with a freezer, wine cellar or holiday home
The five types at a glance
The following descriptions are general. Individual devices may do more or less. Always check the details given by the provider in question.
1. Thermometer and paper log
A person reads a thermometer and writes the value, date, time and initials in a log. A min/max thermometer also shows the lowest and highest value since it was last reset. The US Centers for Disease Control and Prevention (CDC) points out that a min/max thermometer only shows the coldest and warmest temperatures, not when or for how long a value was out of range. A paper log needs no technology and no power, but a deviation is only noticed at the next reading.
2. Data logger to read out
A data logger measures at a set interval and stores the values in the device. It is typically read out via USB and software on a computer, depending on the device also on a display on the logger. According to the CDC, a digital data logger provides details on all temperatures recorded at the set interval, and therefore also on how long a unit was out of range. Some loggers have a local alarm with sound or light. A stand-alone data logger typically does not alert anyone remotely. According to ICOM Switzerland, most of these devices run on batteries.
3. Wi-Fi sensors with app or web portal
The sensor sends its values over the local Wi-Fi and the internet to a server. There you see the history in an app or a browser. If a value leaves the limit, depending on the provider an alert is sent by app, email or SMS, also to several people. This requires Wi-Fi reception at the measuring point, a working router and an internet connection. If the power fails, the router typically fails too, unless it is connected to a backup power supply. Whether a sensor buffers readings and sends them later varies by device.
4. Wireless sensors with a gateway that has its own mobile connection
The sensors send their values by radio to a gateway on site. The gateway forwards them to a server over its own mobile connection. No Wi-Fi and no access to the company network are needed. Depending on the provider, alerts go to several people by app, email or SMS. The limits of this type: the gateway needs mobile reception where it is placed, and it needs power. How long it keeps running during a power cut and whether the sensors buffer readings varies by provider. Frigo belongs to this type.
5. Building management systems and refrigeration controller alarms
Depending on the installation, cold rooms, refrigerated cabinets and air-conditioning units have their own controller with a temperature display. Depending on the system, it raises an alarm on the unit in the event of a fault or passes it to a building management system, the facilities team or a service company. In a practical example from ICOM Switzerland, the building management system alerts facility management by email when deviations are too large. For museums, however, ICOM Switzerland distinguishes between measurements used to control a system and monitoring focused on the objects: according to ICOM Switzerland, the two complement each other but cannot directly replace each other.
Comparison: who notices a deviation
| Type | Who notices a deviation, and when | Alerting several people | History and record |
|---|---|---|---|
| Thermometer and paper log | Whoever takes the reading, at the next reading | No, only whoever is on site | Handwritten log of the values read |
| Data logger | Whoever is on site, if the device has a local alarm, otherwise only at read-out | Typically not remotely | All values at the set interval, visible after read-out |
| Wi-Fi sensor | The named people, as soon as the value arrives via Wi-Fi and internet | Depending on the provider yes, by app, email or SMS | History in app or web portal, export depending on the provider |
| Wireless with mobile gateway | The named people, as soon as the value arrives via the gateway | Depending on the provider yes, by app, email or SMS | History in app or web portal, report depending on the provider |
| Building management, controller | Depending on the system: display on the unit, local alarm or alert to the facilities team or a service company | Depending on the system and how it is connected | Depending on the system. According to ICOM Switzerland, control data are often archived only to a limited extent. |
Comparison: when Wi-Fi, power or a device fails
| Type | Wi-Fi or internet fails | Power cut | Device stops sending or measuring |
|---|---|---|---|
| Thermometer and paper log | Not affected | The thermometer typically keeps showing values, but nobody knows until someone reads it | Only noticed at the next reading |
| Data logger | Not affected | Mostly battery-powered, keeps recording | Noticed at read-out or on the display. For vaccine loggers, the CDC recommends a low battery indicator. |
| Wi-Fi sensor | No alerts while the connection is down. Whether values are sent later varies by device. | Without backup power the router typically fails, and with it the alerts | Depending on the provider, an alert is sent when a sensor goes silent |
| Wireless with mobile gateway | Not affected. Mobile reception at the gateway is needed. | Depending on the gateway, a built-in battery keeps it running for a limited time | Depending on the provider, an alert is sent when a sensor or the gateway goes silent |
| Building management, controller | Depending on the system | Depending on the building's backup power | Depending on the system |
Comparison: day-to-day effort
| Type | Reading and recording | Installation |
|---|---|---|
| Thermometer and paper log | Read, write down and initial at every check, and keep the logs | Place or hang the thermometer at a representative spot |
| Data logger | Read out regularly, file and evaluate the data | Low, depending on the device with software for read-out |
| Wi-Fi sensor | Values arrive automatically. Limits and recipients need to be maintained. | Wi-Fi reception at the measuring point and login details needed, in a business possibly coordination with IT |
| Wireless with mobile gateway | Values arrive automatically. Limits and recipients need to be maintained. | Place the sensors, power the gateway, mobile reception at the gateway needed |
| Building management, controller | Depending on the system, for example via the facilities team or a service company | Planning with a specialist company, depending on the building |
What none of these types does
- None of them cools. Monitoring reports a deviation, it does not fix it. A person has to respond.
- Measurement happens where the probe is. According to the CDC, standard thermometers typically measure air temperature. A probe in a buffer, such as glycol or glass beads, reflects the temperature of vaccines more accurately, according to the CDC. Only a probe in the food measures the core temperature of food.
- None replaces self-checks or official controls. What has to be recorded follows from your own food safety or quality plan and the rules of your sector.
Would you notice if your cold room warmed up on a Saturday evening?
Get your setup →What authorities expect, by sector
The following examples show how differently authorities describe what measuring devices should do. Each applies only to the sector and country named. Check which rules apply to your business. If in doubt, the competent authority decides.
| Sector, country, body | What it says about monitoring |
|---|---|
| Vaccines in medical practices (DE, STIKO at the RKI) | Check the storage temperature regularly, ideally morning and evening, at least once a day. Suitable are a digital thermometer showing minimum and maximum temperature or a thermometer data logger that measures continuously. Alcohol or mercury thermometers, bimetal or infrared thermometers should not be used. Record the results daily. |
| Vaccines (US, CDC) | A digital data logger in each storage unit, recommended with features including a probe in a buffer, an alarm for out-of-range temperatures, a low battery indicator, a display of current, minimum and maximum temperature and a logging interval of at least every 30 minutes. Each device should have a current and valid certificate of calibration testing. Check and record minimum and maximum temperatures at the start of each workday. Keep at least one backup device. |
| Medicine fridges (CH, Canton of Basel-Landschaft) | Record storage, temperature deviations and the measures taken. File calibration certificates for the thermometers or probes and present them at inspection. |
| Wholesale distribution of medicines for human use (EU, GDP guidelines) | A temperature mapping exercise before premises are used. Monitoring devices mainly where the greatest fluctuations occur. Calibrate devices regularly, traceable to a national or international measurement standard. Alarm systems should signal deviations from the predefined storage conditions. |
| Quick-frozen food (DE, TLMV) | Measure and record the air temperature in storage facilities during operation often and regularly enough for the temperature history to be traceable. For small freezers in retail used to store reserve stock, at least one clearly visible thermometer is enough. |
| Catering kitchens and communal catering (AT, hygiene guideline) | Check the temperature of fridges and freezers daily and keep records. State the target range for each unit. Use recording thermometers and check regularly that they work. |
| Museums (CH, ICOM Switzerland) | Data loggers as stand-alone devices or in a network that can be read remotely in real time. Install networked devices only if rapid intervention in case of network faults is permanently ensured. Automatic local backup of the readings is advisable. Check the calibration of humidity sensors yearly. |
More on individual sectors is in the guides to the HACCP temperature log, vaccine storage in practices, medicine fridge monitoring, cold room monitoring, server room monitoring and museum climate monitoring.
Which fits whom
- Thermometer and paper log fit where someone is on site every day, takes readings and can respond, and where the rules of your sector only require reading and recording. For many households, a thermometer in the fridge is enough.
- A data logger fits where the history matters but no immediate remote alert is needed, for example during transport, as evidence after the event or as a second, independent measurement.
- A Wi-Fi sensor fits where there is reliable Wi-Fi at the measuring point and you want remote alerts, for example at home or in a small office.
- Wireless sensors with a mobile gateway fit where nobody is on site at night and at weekends, where there is no Wi-Fi or IT does not want devices on the company network, and where several people should be informed.
- Building management and controller alarms are worth using where they exist. Check who receives the alarm outside working hours and whether the data are sufficient for your records.
The types are not mutually exclusive. The CDC, for example, recommends keeping at least one backup device in case the primary device breaks or needs calibration. What to do when a freezer loses power is covered in the guide on freezers and power cuts.
Questions to ask any provider
- Through which channels does an alert arrive: app, email, SMS or phone call?
- Who receives alerts, and how many people can be named, including for nights and weekends?
- What happens during a power cut? Does the device keep running, for how long, and is an alert sent?
- What happens if Wi-Fi, internet or the mobile network fails? Do the sensors buffer readings?
- Does the system alert you when a sensor or the gateway stops sending data?
- How long does the battery last, who replaces it, and are you told in advance?
- How do you get your data: a PDF report, an export as a spreadsheet, and how long are the data kept?
- Is there a calibration certificate, if your sector requires one, and how often is calibration done?
- Does the sensor measure the air, or is there a probe for the product or a buffer?
- Where are the data stored?
Where Frigo fits
Frigo belongs to the fourth type: wireless sensors with a connectivity unit that has its own mobile connection. The sensors stick on, with no drilling and no cables. They measure air temperature and relative humidity at the sensor's location, not the core temperature of a product. One connectivity unit per site plugs into a power socket, so no Wi-Fi is needed.
You set an upper and a lower limit per sensor. If a value leaves this range, Frigo alerts all the people you have named by app and email, with SMS as an additional option. Every deviation is written with start, end and duration to a continuous, time-stamped record. Alerts can be commented on and acknowledged. A PDF report shows limits and deviations. If a sensor or the connectivity unit stops sending data, Frigo alerts the named people.
The limits: the sensors run on their own battery and do not store readings. Frigo replaces a sensor before its battery runs out and informs you beforehand. The connectivity unit needs mobile reception at the site. If power fails, the connectivity unit keeps running on its built-in battery for about four hours. During that time Frigo keeps measuring and alerts you when a value leaves your limit, as long as the mobile network is available. Once the battery is empty, Frigo reports that the connectivity unit has stopped sending data. The sensors do not store readings, so there is no data for that period. New readings arrive once the connectivity unit has power again. If you expect automatic local backup of readings, as ICOM Switzerland advises for museums, take this into account, for example with an additional data logger.
Frigo does not cool. It replaces neither self-checks nor official controls. If your sector requires a calibration certificate or a particular measurement accuracy, please ask us directly before you start, as you would with any other provider. Answers to further questions are in the FAQs.
Frequently asked questions
Is a paper log enough for temperature checks?
That depends on your sector and country. The Austrian hygiene guideline for catering kitchens, for example, requires daily checks with records and recording thermometers. In Germany, according to the TLMV, at least one clearly visible thermometer is enough for small retail freezers used to store reserve stock. A paper log only shows a deviation at the next reading. The competent authority decides.
What is the difference between a min/max thermometer and a data logger?
A min/max thermometer shows the lowest and highest value since it was last reset. According to the CDC, it does not show when or for how long a value was out of range. A data logger stores every value at the set interval. From this you can see when a deviation started and how long it lasted.
What happens to a Wi-Fi sensor if the power or internet fails?
As long as Wi-Fi, router or internet are down, alerts typically do not get through. During a power cut the router typically fails too, unless it is connected to a backup power supply. Whether the sensor buffers readings and sends them later varies by device. Ask the provider.
Do I need a calibration certificate?
That depends on your sector. In the US, the CDC expects a valid certificate of calibration testing for vaccine monitoring devices. The Canton of Basel-Landschaft requires calibration certificates for the thermometers or probes of medicine fridges to be available at inspection. The EU GDP guidelines require regular calibration in the wholesale distribution of medicines. Ask every provider directly whether they supply a certificate.
Does a temperature sensor measure the temperature of the goods?
Not automatically. A sensor measures where its probe is, usually the air. According to the CDC, a probe in a buffer, such as glycol or glass beads, reflects the temperature of vaccines more accurately than a thermometer measuring the air. Only a probe in the food measures the core temperature of food.
Does a monitoring system alert me when a sensor fails?
That depends on the type and the provider. With a thermometer or data logger, a failure is typically only noticed at the next reading or read-out. Systems with remote alerts can report when a sensor stops sending data, but not all of them do. Ask the provider.
Does Frigo work during a power cut?
Yes, for a limited time. The connectivity unit has a built-in battery and keeps running for about four hours during a power cut. During that time Frigo keeps measuring and alerts you when a value leaves your limit, as long as the mobile network is available. Once the battery is empty, Frigo reports that the connectivity unit has stopped sending data. The sensors do not store readings, so there is no data for that period. New readings arrive once the connectivity unit has power again.
Sources
- Centers for Disease Control and Prevention (CDC): Vaccine Storage and Handling Toolkit, section Temperature Monitoring Devices (July 2026, USA)
- Robert Koch Institute: Recommendations of the Standing Committee on Vaccination (STIKO) at the RKI 2026, Epidemiologisches Bulletin 4/2026, chapter 4.4 (22 Jan 2026, Germany, in German)
- Canton of Basel-Landschaft, Medicines Department: Fact sheet on the qualification of medicine fridges (version 01, March 2024, Switzerland, in German)
- European Commission: Guidelines on Good Distribution Practice of medicinal products for human use, 2013/C 343/01, sections 3.2.1 and 3.3 (23 Nov 2013, EU, German language version)
- Federal Ministry of Justice: Ordinance on quick-frozen foodstuffs (TLMV), section 2a (Germany, in German)
- Hygiene guideline for catering kitchens, healthcare kitchens and comparable communal catering facilities, chapter 6 (GZ 2025-0.879.838 of 4 Dec 2025, Austria, in German)
- ICOM Switzerland: Recommendations for climate monitoring in museums, chapters 4 and 5 (12 Dec 2024, Switzerland, in German)
How Frigo works in detail
Sensors, connectivity unit, alerts and record: see how Frigo is built and what it does when something fails.
How Frigo works →This article is guidance, not legal or professional advice. It names no specific products and describes typical properties of each type, which can vary by device. Requirements differ by sector and country; the competent authority decides. Frigo measures air temperature and humidity at the sensor's location, does not cool and replaces neither self-checks nor official controls. Alerts require a working connection. During a power cut the connectivity unit keeps running on its built-in battery for about four hours, after that Frigo reports that the connectivity unit has stopped sending data. Sources as of: October 2026.