[EquitableEngineer]

What is the best way to back out if it fails?

Just some BS like 'my housemate took it out of the box and hid as a prank', just make sure whatever you say lines up with what you have already said. If you have not used it and said 'my housemate took it out of the box and has been using it the whole time and I only just got it back and want to return it' then they could see that the device had not been activated and your story would fall through.