We have a dog (rescued from a puppy mill) that goes to the back door when she needs to go out, but she doesn't make any noise. After a couple of minutes, she does her business right by the back door. :-(
What I think that we need is some kind of sensor that detects her presence by the door and rings a remote alarm, so we can let her out before it's too late.
Is anything like this available as an off-the-shelf consumer product? The alarm should preferably be wireless and with a range of at least 20 feet.
What should I search for? All I can find are expensive burglar alarms.
I am comfortable with building a suitable circuit from the ground up. But I would rather not do that, as we need an immediate solution for this dog's changed behavior.