Worry-Free Hallway Sealed Lithium Battery Power Smoke Alarm  P3010H Ideal for hallways with 10-year sealed lithium battery and emergency exit light to guide you to safety Hassle-free protection - Goodbye late night low battery chirps! Never replace a battery during the alarms operating life and no need to worry about the batteries being removed Always on - Sealed-in lithium battery powers alarm for 10 years - the life of the alarm The right alarm, the right location. - Each of the four smoke alarms includes features designed to address location-specific safety needs, such as an LED light in the hallway Photoelectric Sensor  Advanced photoelectric sensor may detect visible particles (associated with smoldering fires) sooner than ionization alarms