Keypads of home security devices from Ademco and Honeywell
Normally (if a wired alarm) the battery is in the alarm system box (typically a 12V gel-cell or AGM lead-acid battery.) If wireless, every [expletive] thing will have a battery to replace.
For reset instructions look up the model of the main alarm panel (not the keypad) for instructions. Start with the lazy option of &quot;try the factory default&quot; since many people don't bother to change them.