OK, got my hands on the device this morning. It had gone to sleep/turned itself off again so I looked in the app which said it was offline. This is what I did next.
I shook it to see if tamper alarm woke it up. It didn't.
Quick tap in left hole didn't wake it up.
Tap and hold didn't wake it up.
Connected it to power, it didn't wake up.
Tap and hold when connected to power woke it up.
Check in app for battery percentage, is at 21% as soon as it appears in app
Sleep time is set to 0
So maybe the battery was low although I'm pretty sure I charged it fully before installing.... I've put it back in place after making sure the battery is at 100%, lets see what happens next!