Williams Sound PLR BP1 Proloop Body Pack Induction Loop Receiver, Black ABS/Polycarbonate Molded Plastic Case, Frequency Response 300Hz to 10KHz, Internal Tone Control, 3.5mm Stereo Jack Operates up to 200 hours with two AA alkaline batteries Simple to use - on/off volume control Internal tone control, 3.5mm stereo jack External switched thumb wheel controls power on/off and volume level Compatible with Williams Sound 2- and 12-bay chargers (CHG 3502 and CHG 3512). Chargers sold separately