Features: 433MHz frequency, compatible with wireless video doorbell. Plug-in chime, easy to use, designed for indoor use only. Adjustable volume, low to mute, up to 110dB. Different melodies for selection, meeting various needs. A chime can pair with multiple doorbells, a doorbell can pair with multiple chimes. Note: Size and color may be slightly different due to manual measurement and different light conditons or other reasons, please in kind prevail. Thanks for understanding.