NFPA 13 2010ed. 6.9.3.1 "An alarm unit SHALL include a listed mechanical alarm, horn or siren, or a listed electric bell speaker, horn or siren."
From that, we know that a bell is required somewhere on the premises.
A6.3.9.1 "Audible alarms are normally located on the outside of the building. Listed electric gongs, bells, horns or sirens inside the building, or a combination of such used inside and out, are sometimes advisable. Outside alarms might not be necessary where the sprinkler system is used as part of a central station, auxilliary, remote station, or proprietary signaling fire alarm system, utilizing listed audible inside alarm devices.
The commentary from the 13 handbook states "The audible local alarm required by 6.9.3.1 can either be mechanically or electrically operated. NFPA 13 does not stipulate whether the alarm's location is to be indoors or outdoors, since the location depends on site specific conditions.
Clear as mud?
8.17.1.1 backs 6.9.3.1 by stating "A local waterflow alarm shall be provided on every sprinkler system having more than 20 sprinklers.
So the answer to your question would be, no, there is not a requirement for an EXTERIOR water flow device.
Unless of course you're talking high rises, where we would apply 8.17.2.6(1) ...The annunciator or register shall be located at grade level at the normal point of fire department access, at a constantly attended building security control center, or at both locations.
I've always shown an exterior bell on my plans, right above the FDC. If the building owner doesn't want it there, or the sparkies don't want to run more conduit, I'm happy to put it anywhere suitable to the AHJ.
