It's not that my smoke alarm is hard to reach, or that I don't have a spare 9V battery around. But doesn't this doo-hickey make a lot more sense? Plant the alarm in a light socket, then screw the bulb in. Everytime the light is turned on the alarm charges. Flip the lightswitch twice to test the alarm, and three times to shut the thing off. Will operate for 30 days without charging, and chirps when it's running low on juice. Ugly as sin if you've got low ceilings—but a small price to pay in exchange for crossing the annual battery replacement ritual off your list. $39.95.