If the alarm uses a push button to switch on the scream and spray devices then it could be easy to interface them.
But check the legality of remotely imobilising a car that is being driven. And the legality of "attacking" the criminal driving it. Either of those could result in the driver losing control and causing an accident involving injury and maybe death to other innocent road users.
If your car has a tracker then register it with one of the tracking services and they will, if their terms and conditions are met, alert the police to the vehicle's location.
Many years ago, one of the diy electronic mags had a project to build an "intermitant immobiliser". It worked by letting the engine run for 5 seconds, immobilising for 5 seconds, let it run again for 5 seconds, and so on. The theory was that no one would want to steal a temperamental car.
I always liked that idea but that was in the days when an FS451 key would open most cars and could be bought at the local parts shop...
My preference would be to have a real time trakker that would tell me precisely if they were stationary or not. The siren/spray are, to my knowledge, entirely legal as they are available for anyone to use in the event of an attack.
Thus, immobilisng the car, enabling it to be recovered safely whilst attempting through sound for the thief to leave the vicinity (with ths chock factor enhancing the chance of him/her leaving anything else stolen in the vehicle) and also marking him/her to enable an increase chance of arrest surely would be a sound and sensible resolution to the situation.