A lot of it will depend on what's already installed.... or what equipment you're getting your contact closure from... whether it be a radio, or an amp-charger base for a Minitor pager, etc...
This is a great resource I used to set up our station bell/strobe/PA system. Includes information on timing relays and even adding a tone generator and boosting the volume during pages, and lowering it during non-page audio. Pretty in depth.
We went pretty simple when I did the one at ours... it's a Minitor amplified charger. The pager is set to auto reset after tone-out, rather than remaining open. When the tones drop, the contact closure in the pager base trips two timed relays. The first is a relay which sends 12vDC to our house bell for the duration of the alert (3-4 seconds, usually). The second relay activates the strobe lights on our station speakers (fire alarm system strobe/speaker ceiling mount) for about 10 seconds. The word "FIRE" was replaced with "ALERT" to avoid confusion of the strobe.
Our audio for the page is sent to the speakers, and gradually ramps up during the alert phase of the tone out.
All in all... not a bad little system for a weekend project. We also included another set of relay contacts to turn on bunkroom lights and hallway lighting if we choose to have a staffed crew in the future. Those would trigger the lighting contactor in the appropriate rooms and activate the lights for 90-120 seconds.
Fire Station Alerting System Design