How the fuck do I open this keyfob to change the battery?

Unless I'm completely blind there's no visible screw holding it together. I could potentially jam a small flathead screwdriver in the join at the bottom portion and pry it apart but a careful test run to see how that'd go felt very dangerous and this thing is too expensive to risk damaging it.

It's for a wireless home alarm system, I think it's an Enforcer v11 or at least it looks like one. Thanks for any help.