Kidde PE9 (P9050) Battery-Operated Photoelectric Sensor Smoke Alarm Advanced photoelectric sensor is especially effective in detecting smoldering fires Battery backup 9V battery included (best with Polaroid 9 Volt batteries) Battery pull tab eliminates battery installation time and keeps battery fresh Quick connect power harness makes installation fast and easy Kiddes smoke alarms meet the requirements of Underwriters Laboratories (UL), an independent facility that tests products for compliance with widely-accepted safety standards