Smoke alarm low battery beep at random.It needs to be subtle, quiet, every so often a noise appears that could come from anywhere.
Then do this for several weeks
This is evil. But brilliant.Smoke alarm low battery beep at random.
You would have to record descriptions of what you think they are doing, such as.
"Subject B114 watching TV"
"Subject B114 has put the washing machine on"
... and so on
That would freak them right out.
Bit of a long shot but given that if they own a mobile phone, chances are it's going to be either a iPhone or Samsung, gamble that it's a samsung and use the Android/Samsung "new message whistle" sound. They could potentially be checking their phone a lot more often than they should be![]()