I banged up villains for near on 30 years, so I know where of I speak.
An opportunist will be put off by the padlock in the first place. Theyre after insecure bikes left in public - opportunists do not take locked bikes - and will stroll up and push it away is if they were entitled and nothing was amiss. An alarm would make zero difference to that scenario as the lack of padlock is their only concern.
A run of the mill thief wont give a sheet about anything except the lock. Not cctv, not alarms, not property marking. There is even evidence (there was a study where many thieves were interviewed) that the presence or the police wont deter them provided the bobby isnt actually right next to the bike. All theyll care about is whether theyre able to defeat the lock in smart time so they can be on their way before people get suspicious. An alarm makes zero odds if they can crack the lock and be on their way in 10 or 15 seconds max before people really twig whats going on, and will happily ride the bike (or indeed motorbike) away with the alarm still audibly wailing.
And then theres the small but significant class of thieves prepared to use disproportionate levels of violence against anyone who interferes in order to achieve their goal. Theyll be tooled up, mob handed, and will often use battery grinders and the like because they have sufficient muscle on their side they don't care about stealth. An alarm to them is as much deterrent as a feather duster.
Those are the 3 main groups, and none will care about any alarm.
