Supposedly you can test for this using a wifi device since the frequencies are similar so I threw this together https://ismymicrowaveleaking.isotropic.us https:

Supposedly you can test for this using a wifi device since the frequencies are similar so I threw this together https://ismymicrowaveleaking.isotropic.us https://ismymicrowaveleaking.isotropic.us if anyone wants to try it. No clue how accurate it is, seems to work for my sample size of 2 microwaves. Phone had to be on 2.4ghz wifi or the signal was unaffected.