Review on Wireless Doorbell, PHYSEN Waterproof Door Bell Chime Kit Operating At 1300-Ft Range 58 Adjustable Melodies 5 Volume Levels & LED Flash, Doorbell Alarm For Home/Classroom, 2 Push Buttons+4 Receivers by Timothy Castillo

I was skeptical before purchase, but impressed after install. Volume options include very loud for those who need it. Mine are down one notch or two depending on location. Wireless range works well upstairs, main floor or basement. Several "normal" doorbell sounds to chose from in addition to a bunch of songs I can't imagine using. Easy to program second transmitter to different sound for back door/ side entrance. Can use (US) 2 prong power outlet, and the second is not blocked.My only concern is the transmitter case (push button) was a bit hard to open, and once mounted, the included battery may be difficult to replace in a couple years.