How necessary is the deep model there? It seems like a simple motion detector would work just as well since he doesn't mention using the lawn himself.
https://www.tensorflow.org/mobile.html
http://mxnet.readthedocs.io/en/latest/how_to/smart_device.ht...
1) set the motion detection area only on the lawn 2) Set a delay for like > 30s movement 3) Set times of movement (ie. when they're at work)
But the big question is: did it work ?
One simpler way to go IMO would be to put the system at ground level and use two motion detectors, one aimed specifically to "see" only things that are a meter or more above the ground. Humans would trigger both, but the cat would only trigger the one aimed at the ground.