KabaMas 552 locks don't need a battery!

My FIL passed away a couple of weeks ago. My wife inherited the house and contents. Found a Sentrysafe (barcode x055g0700511214) on the side.

The front has a keypad with 3 lights (all non-working red green yellow) as well as a key hole marked x54 and a dial.

I can't find a spot for batteries and have no idea where the key could be.

Any help would be appreciated.

Thank you.