Electric door bells, Wireless Doorbell 2 Waterproof Transmitters and 4 Plug-in Receivers | CoolqiyaDescription Long Range Transmission up to 1000ft in open air. Wireless Multiple Door Bells Chimes Easy to expand door bells or chimes. You can expand extra 10+ door bells or receivers. 52 Different Ringtones and Four levels Volume to Adjust and they will keep the settings when power is removed, no need to reset. IP55 Waterproof; with CE, FCC, RoHS certified. Strong Working Signal for most material door or wall, including glass, metal, wood and more.