Given an IP address it will ping at 1 second intervals and trigger an IFTT event if the device becomes available I'm using this to detect my Amazon dash buttons, but you can use for phone/watch/bathroom scales detection in the same way.

You'll need to set up static ip addresses for the devices on your router so that they always get the same one.

You also need to get a IFTT maker key

To use:

docker run --restart-always -d \
  -e IFTT_KEY=YOUR_IFTT_MAKER_KEY \
  -e DEVICE_button121=192.168.0.121 \
  -e DEVICE_button120=192.168.0.120 \
  -e DEVICE_weighin=192.168.0.122 \
  chrisns/ifttt-ip-presence

In this example I'm waiting for two dash buttons on 192.168.0.121 and 192.168.0.120 and I will fire the trigger button121 and button120 that I setup in IFTT. I've also got a bathroom scale and I trigger a weighin event when 192.168.0.122 is present.

Notes:

• Theres a weird thing on docker for mac where pings always get a response irregardless of where they're going, so it won't run on that (at time of writing)
• For getting the Amazon dash buttons to register to your wifi without buying stuff see https://blog.georgevanburgh.co.uk/2015/10/18/hacking-amazon-dash-buttons-in-the-uk/
• The backoff for running the event again is 5 seconds, if you need a longer backoff you can set -e SLEEP=10 for a 10 second backoff time