If someone really wants to nick your bike, they will, especially the pro's.
Alarms cause nothing but electrical issues.
Old school meaty chains are the best deterrent.
It's good to prevent kids from climbing the bike and burning/harming themselves.
It's also a deterrent. All things being equal, thieves go for the bike without an alarm.
But I agree that a chain is a lot more effective - garage being the best thing.
However, as an addition to a good chain, alarm is not too bad IMO - if you don't have a garage especially.
An alarm doesn't prevent kids from doing anything?
Twice now i've seen youngsters on scooters, no doubt nicked, hurtling down the pavement, and in traffic, with no crash helmets on at all.
First time was 2 scooters doing 30-40mph on the pavement with one and two kids on them, wearing bandana's over their faces.
And near my work the other day another one, about 16yrs old, brazen as anything, just riding on the road, again with no hint of a crash helmet, with a stinking attitude face on him.
They simply don't give a shit, and have now found out that the police have been told not to touch them if they have no crash helmet on, so they're abusing the fact, and going out robbing people in the streets using these bikes.
I personally would have taken a much different approach which would undoubtedly not end too well on their part, but unfortunately that's not my decision to make.