Will alarm going off drain car battery?

I’m sat on a cross channel ferry and can hear a couple of car alarms going off and being a paranoid type I’m hoping one isn’t mine (I followed the instructions to lock the car without the alarm by pressing the lock button twice, but there’s no confirmation that the alarm is disabled!). However will a car alarm totally drain a car battery (it’s a 3hour crossing) or do they stop after a while to save the battery?

They usually cut off after a set time, and reset, but if they keep tripping, they will go on and off.
If that happens it could drain the battery, but for a 3 hour crossing you should be ok
One relax and go outside and look at the beautiful sea

As above, but with the added comment that the ports all have small forklift type of things with jump leads. If your battery is flat they will bump or jump start you for free. Not doing so would slow the unload/load process down and they don’t want that.

I think the ferries are used to this, last time there were chaps walking around with battery rigs on sack trucks, so I think you will be OK.
Slightly different issue, but I have had a car (12 yr old Saab) sitting on the drive not being used for a couple of months and the battery drained to a low level which caused the alarm to set off (low setting in case wires cut and independent battery for alarm still works!) and it went off at mid-night, cue me running around outside trying to shut it up!

3 hours is fine

DFDS on the newcastle-amsterdam route call people over the PA to publicly humiliate them and tell them to go disable the alarm.

Superferries on Rosyth-Zeebrugge (RIP) didn’t and all I could hear all night long were car alarms going off. Better than the cabaret though I guess.