The four (4) inch unit is smaller in diameter giving it discreet design with the same quality you would expect in a Kidde manufactured product. The i9040 is powered by a 9V battery, providing continuous protection, even during power outages. This easy to install unit includes a test button to verify the detection electronics are working as intended. Consumer Benefits The Fire Sentry i9040 battery operated, single station smoke alarm provides an early warning signal to you and your family in th