I would just use extra variable alarm_state; at beginning of cfg set it to 1. After you near level exit use trigger ( one i used in my script teledemo for example ) to set alarm_state to 0. Make your script so that alarm only sounds if alarm_state is 1 (simple if (= alarm_state 1) [alarm..][] would do; or maybe just clear alarm function with alarm_function = []; or just use clearsleep ). This will work in all game modes if your alarm function works too.

Yeah, use /clearsleeps as Ac said :P

you can also use loopwhile, and by attaching it to a trigger near the end of the game will get you what you need. clearsleeps cansels all running loops so its probably not the best idea..