The Tattletale Adjustable Temperature Sensor is designed to trigger an alarm condition if the temperature rises above or falls below your temperature settings. The unit has a high range of 299°F and a low range of -58°F. The sensor can also be programmed to a supervised 24-hour zone to notify the central station whether the Tattletale base unit is armed or not. This unit requires AC power - but has a backup battery that will typically last 12 hours.