X-Sense Hardwired Combination Smoke and Carbon Monoxide Detector, Hardwired Interconnected Smoke and CO Detector Alarm with Replaceable Battery Backup, XP04, 3-PackBrand: X Sense Features: More Accurate with Intelligent Technology: This hardwired smoke and carbon monoxide detector combines an advanced photoelectric smoke sensor and a Figaro electrochemical CO sensor to detect smoke from smoldering fires and dangerous CO levels quickly Hardwired Alarm with Replaceable Battery Backup: This combination smoke and carbon monoxide detector is AC hardwired with a 9 V battery backup, so the alarm can continuously