alan_m was thinking very hard :
Judging by the keys for a couple of up and over garage doors I've encountered
the locks fitted to many garage doors are of the low quality, low security
type.

Yes, just a simple flat key, probably easy to pick.

The roller doors are a little better, but difficult to make anything
proof against a determined attack. All you can do is ensure a lot of
noise is involved in breaking in and getting through a roller shutter
woud be a very noisy exercise..