Just saw this doorbell...
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I’m a little surprised this nifty little wireless device is not more commonly used, as the typical doorbell is not as easily accessible to most household pets. According to comforthouse.com, it is possible to use the Pet Chime both indoors and outdoors, so that the pets can inform their owners when they would like to be inside or out.
The “paw” component of the Pet Chime operates on a 9-Volt battery, while the ringer operates on three AA batteries.
The price range is about $25-$30 USD.
Doorbells for Dogs - Pet Chime