Designed to accurately monitor the temperature of mission critical refrigeration units, ensuring that the contents remain at the critical temperature required for your application. The ISL125Q is battery powered, wireless and simple to install at any location.

  • Temperature: -40 to +125°C, accuracy: ±0.25°C (typical) from -40°C to +125°C±0.5°C (maximum) from -20°C to +100°C±1°C (maximum) from -40°C to +125°

  • Sensor is equipped with 1m long cable with SS probe

  • Measurement period: 30 seconds to 60 minutes (configurable by user)

  • Ability to incorporate up to 4 temperature probes

  • Battery ensures up to 5 years of maintenance-free operation

  • Use Real-Time Online for a personalised, real-time monitoring system 

105Q - 45 Deg


battery (1)

Long Battery Life

Our sensors have been designed to have a battery life of up to 10 years, so you don't have to worry about changing them frequently.

bell (1)

Proactive Alarm System

Pro-active alerts ensure that your team can prevent temperatures breaching critical levels, and so safeguard patient well-being.


Improved Patient Safety

By ensuring that your medical fridges are always at the correct temperature, you improve the potency and reliability of medications and vaccines.

website (1)

Real-Time Online

Together with Real-time Online, the sensors enable constant monitoring, deliver pro-active alerts on threshold breaches and generate bespoke reports.

two-settings-cogwheels (3)

Simple Set-Up

Pro-active alerts ensure that your team can prevent temperatures breaching critical levels, and so safeguard patient well-being.


Low Costs

Choosing wireless sensors and a cloud platform enables you to reduce your installation and maintenance costs.



Configurable high/low thresholds allow different transmit intervals when thresholds are crossed providing advanced edge intelligence to the network, and enable alarms to be generated by Realtime-Online™.


Data from every sensor in your network is reported back through Invisible Systems Big Data architecture either to our Monitoring and Analytics platform Realtime-Online™, or to a partner cloud platform via our API, ensuring that your data is visible, actionable and valuable to your organisation.


Data NB-IoT is a standards-based narrowband Low Power Wide Area (LPWA) technology developed to to enable a wide range of new IoT devices and services. NB-IoT devices connect directly to the cellular mobile network via a low-cost SIM card. NB-IoT significantly improves the power consumption of user devices, system capacity and spectrum efficiency. 



Band: 1, 3, 5, 8, 20, 28

Expected range (line of sight): Up to 10km

Power: 23dBm ± 2dB


CE, other regions available on request


Dimensions (mm): 144x65x40

Enclosure colour: Black

Enclosure plastic type: ABS

Operating Temp Range: -20°C to +60°C

Battery: 1 x C-cell (8500 mAh)

Batteries type: Lithium Thionyl Chloride (Non rechargeable)

Expected battery life, 6 min Tx interval: Up to 3 years

Expected battery life, 6 hour Tx interval: Up to 10 years

Operating lifetime: Up to 10 years

Power type: Battery 3.6VDC


Measurement interval range: 30 secs - 60 mins

Tx interval range (multiple of measure intervals): 15 min - 24 hours



Measurement Range: -40°C to +125°C


  • ±0.25°C (typical) from -40°C to +125°C
  • ±0.5°C (maximum) from -20°C to +100°C
  • ±1°C (maximum) from -40°C to +125°C

Resolution/Step-size: 0.1°C

Sensor characteristics: Digital

Calibration: Optional



Temperature probes: Up to 4 - any combination of Pipe & Stainless steel pocket (submersible) probes

Cable: 1m PVC Ribbon



Digital status inputs: 2

Cable: 1m 4-core PVC (optional)



Download Datasheet
We wanted to use the IoT approach to technology using a device placed in a fridge to allow us to continually monitor temperature, but also to flag up where breaches occur so we can respond to them then and there. We now have evidence to show that, 24 hours a day, our vaccines are being stored at the correct temperature Paul Brown, NHS Suffolk Primary Care
We were looking for a wireless system, one that allowed all users to log on from off-site, was flexible enough to allow grouping per PI of units and didn’t need dedicated server hardware/networking. The trial of the system was so simple and impressive that we kept it. Royal Holloway University
Invisible Systems solution is so easy to install, there is no need to interfere with other IT services. It was a non-invasive install and that was a primary factor in selecting it. I can log in from home, from holiday - it’s very user friendly. Noel Gavin, Maynooth University