SimpliSafe Temperature Sensor will not reset or needs to be reset safely

The checks in more detail

Look in the app for the sensor's status and the reading, and compare it with a thermometer in the same spot. If it still misbehaves, remove it from the system in the app, which clears its pairing, and reset it. SimpliSafe's help page for the temperature sensor describes how to put the sensor in pairing mode, which differs between versions, so follow the page for yours. After the reset, add the sensor again in the app, choose the room, and set the alert thresholds, such as an alert when the temperature falls to the level at which pipes are at risk. Give the thresholds a margin so that you get time to act.

Test it by holding the sensor in your hand or cooling it briefly, noting that the reading changes in the app after a short delay, since sensors report at intervals to save the battery. A sensor that works but lags is normal. A sensor that reports a value that never changes may have lost contact. Keep it within range of the base station. If it will not pair after a reset and a fresh battery, contact SimpliSafe with the serial number, as a faulty sensor can be replaced under warranty. In cold weather, batteries lose capacity, so check them before winter.

A temperature sensor earns its place in rooms where a failure would cost money, such as a basement with a water heater, a crawl space with pipes, a garage with a freezer or a wine cellar. Alerts at the low end warn you of a heating failure before pipes freeze, and alerts at the high end tell you that a freezer or a cellar has warmed. Pick a low threshold that leaves you time to get there, a few degrees above freezing for a pipe, and note that the reading will lag behind the real temperature by some minutes. If you leave the house for the winter, ask someone to check the alerts reach their phone as well as yours.