Kidde 0910 10-Year Sealed Lithium Battery-Operated Smoke Alarm with Memory and Smart Hush (2 Pack) Sealed in lithium battery never replace battery over the ten-year life of the alarm Rapidly flashing red LED alerts the user if the alarm has sounded since the last time the test reset button was used Self activation alarm automatically activates when securely attached to the mounting bracket Kidde's smoke alarms meet the requirements of Underwriters Laboratories (UL), an independent facility that tests products for compliance with widely-accepted safety standards Smart hush temporarily silences nuisance alarms and will not allow hush mode to be activated unless the unit is in alarm mode