Seal, this does work (I use it) even tho countdowns are in it. It's from some tut, I think it was the Edit Ref in PDF format from a ways back. This will give you the delay and seem a bit more realistic.
requires 4 triggers (repeat #3 and #4 for each sentry area, with diff names)
#1 ALARMSOUND (this simulates a bullhorn speaker, I usually put at main base area)
1 x 1 (or whatever)
Repeat
TYPE: none
Present
Countdown (put in what you want, I usually go for between 10-30 secs - those are seconds markers in trig Min/Med/Max)
FX: alarm sound from effects menu
CONDITION: alarm
#2 ALARMOFF (this is the off switch, right next to "alarm")
same as above mostly, but:
COUNTDOWN (however long you want alarm to sound - I always figure in real life somebody'd turn it off after awhile, maybe 30-60 secs)
CONDITION: alarm
ON ACTIVATION: alarm=false
#3 ALERTSENTRY
Repeat
SIZE: as big as the area you want to cover (I use what you can see from the sentry point for distance), usually make elipse so as to not cover obstructions - like a hill or something)
ACTIVATION: West DETECTED by East (like you were saying, because this is more real than an automatic trip)
Countdown
COND: this
ON ACTIV: alertsentry1=true
#4 SENTRY
Repeat
same size as #3, placed right on top of #3
Present
Countdown
CONDITION: alertsentry1 AND ((alive loon1) OR (alive loon2)) AND alive radio1
ON ACTIV: alarm
EFFECT of all that:
West trips trigger, if East detects, after a countdown and at least one loon is alive and the radio is alive, then "alertsentry1" becomes true, and this makes "alarm" true, which makes the actual alarm trigger scream. At same time, the alarmoff trigger starts, but doesn't come into effect for X seconds, and when it does, it turns "alarm" to false, so alarm stops. This is more real as you were saying: East spots West, takes some seconds to make radio call to base (or run to Office or something), then once base gets the alert msg, takes some seconds to turn on alarm itself.
This really does work. You can make more or less complicated. Have a designated radio operator report back to base, etc. I've added a radio, so if West kills just the radio itself, there can be no alarm
The tut talked about making even more complex by putting in a callback thing, where base checks in every 15 mins, if no response, alarm. I haven't opted for that.
I use #3 and #4 for each sentry point, covering an area, rather than just one big trig blanketing everything (beause of the obstructions and the interest of more realism.)
I hope this helps. If you have trouble, I can put it into a tiny sample mission and you can see the countdowns do work. Good luck.