We are fortunate to live in a world with a surplus of Android smartphones. These devices generally have Wifi and Bluetooth radios and work quite nicely even without a service contract with a telephone provider.
Has somebody written an app that lets me use my extra smartphone as a baby monitor (preferably audio and video)? The monitoring phone can sit there in speaker-phone mode with its volume all the way down, and then I can use my phone to listen in. Ideally this would all be encrypted, travel over local Wifi or a peer-to-peer Bluetooth connection inside my house, and be just fine running for 12 straight hours. In this use case it’s totally fine for both devices to be plugged into wall power the whole time.
A second idea is to use an extra phone as a dog presence / bark sensor. When the dog jumps up on the gate and barks at somebody, turn the hose on for about a second. Have the hose hooked to a typical lawn sprinkler. A little localized, on-demand rain should be enough to encourage the dog to stop that. Maybe this is too cruel? Maybe it’s brilliant?
Obviously all of these things can be readily built, but right now I don’t have the time.