Get something like this:
Strobe light from Spencer's GiftsAnd stick it on a code that goes "ON" and stays "ON" during an alarm condition.
Should work just like turning on any other light. Build a box for it with a couple
of mirrors angled at 45-deg to either side so it can be seen by someone coming
up the street from either direction. Add a red filter in front so it shows as an
"emergency light" rather than a bright white annoyance.
Gerald