Cambond (99% positive feedback lifetime) via Amazon has its self-powered 500-ft range wireless waterproof doorbell with two plug-in receivers on sale for $18.99 Prime shipped when code BC77ACVR is used at checkout. Normally $26, this is the lowest we’ve seen this offered for. Perfect if you need to upgrade your doorbell, this allows you to do it without wires or batteries. Rated 4.5/5 stars.
Nomad Base Station
Cambond self-powered wireless doorbell features:
Wireless Doorbell but No Battery Needed for Transmitter: The doorbell button transmitter is used the unique Kinetic technology that generates electric power to ring your home door bell without any battery and create wireless signal, which wire is not required for installing door transmitter and plug-in home receivers (The receivers require outlets.)