First Alert Smoke Alarm With Test Button SA300CN3 The First Alert Smoke Alarm SA300CN3 with test button allows you to test both the sensor and the loud 85decibel horn. It features a low battery alert to remind you when to change the battery and has a missing battery guard to ensure that a battery is placed inside the alarm. The side battery drawer slides open for easy battery replacement. A blinking power indicator on the unit confirms that it is receiving power. The alarm also contains an optional pin to lock the battery and unit in place for tamper resistance. It can be mounted on either the ceiling or the wall and can be used in mobile homes and RVs. It includes one 9volt battery