God i have answered this question 8,000 times.

at the cpu, ground the lt.green/back wire.

 

Sorry for bringing up an old post.
My stock S5 alarm ,no ECU (haltech) and power locks goes off after sitting a few minutes and I am not even locking it. Can someone tell me how it activates?
I know unlocking pass door de-activates it so I am about to just ground that light green black wire that comes from lock cylinder but, why does it get activated in in first place?
Does the alarm get locked signal from the inside door lock or the handles?
Thanks

 

I've got an S5 too. I once had a similar problem. Alarm would trigger randomly as yours is doing. There are microswitches in the outside door handles are, for lack of a better term, slip fit. On my driver's side door handle, the microswitch slightly slipped out position causing the alarm to sometimes trigger. Not saying this is your problem but it might be worth checking out during the trouble shooting process.