Battery-Operated Smoke Detector has a photoelectric sensor for a quick response to slow, smoldering flames Smoke detectors for homes will have either a photoelectric sensor (like this one) or an ionization sensor. A battery-operated smoke detector with photoelectric sensor may respond slightly faster to slow, smoldering flames, while an ionization sensor may respond slightly faster to flaming fires. This photoelectric battery-operated smoke detector includes a test button, 85dB horn, 9V super heavy-duty battery, low-battery indicator, and 5-year mfr's. limited warranty. Meets all building codes requiring photoelectric sensors. The properties you manage almost certainly need several smoke detectors; for homes and offices like those, this battery-operated smoke detector is a good buy! Listed to UL217 Standard. Also includes a separate 5-5/8" mounting plate which attaches to any standard rectangular or octagon junction box and covers drywall cutouts; hardware included.