Wireless & easy to pair with the Yale Sync Home Alarm System. When smoke is detected & alarm is armed, smoke detector triggers the external alarm siren & sends a push notification. Heat sensor will send a heat signal when the temperature changes +/- 2°c, & will trigger the alarm if the temperature rises by 8.25°C per minute, & when the temperature exceeds 57.3°C. Built-in PIR detects motion to trigger alarm when system is armed.