Hi,
I think any sort of single alarm that is visible is a weakness, especially if it can be coated with gap filling foam or similar to muffle it without setting the motion detector off.
House alarms can be silenced like this if they can be seen.
I don't know the answer to the problem of theft apart from deterrents, barriers and locks, and must admit that security by obscurity is probably not going to be my option for much longer.
cheers