Help! Does anyone have the Playmobil police advent calendar

[ThatsNotMyHouseItIsTooClean]

My son opened his this morning & we had a white lump of plastic - possibly a safe? - which looks as though it should open but doesn't. Any ideas? Is it just a white lump of plastic?
I have also asked this on the Christmas bargains thread as I'm curious and what also like to explain it to my 3yo.
Thanks

I have it. It's the working burglar alarm I assume. I haven't had chance to try it though. I think it might need batteries (maybe AAA?). I expect the instruction book will explain all (if I ever find it again!)

Two aa batteries, push the button to activate and it's a motion sensor burglar alarm