Mike,
None of these watches have the barometric rate-of-change (ROC) alarm you are looking for. The various Suuntos and the Casio I use, all have altitude target alarms, not baro rate-of-change alarms.
And there is a very good reason they don't..
These wrist barometers have the info they need to implement such an alarm, but the watch does not know weather a reduction in baro pressure is indicative of an incoming low-pressure storm system, an increase in pressure altitude, or both!
The change in barometric pressure indicative of an approaching storm system is VERY minor compared with the altitude changes a typical mountain hiker would experience.
For example, referring to my desk reference (The Mountaineering Handbook by Connally), we see the following warnings..
1. 40-60 feet "apparent" (as read on a stationary altimeter) altitude gain over 3 hours – mountaineer should watch for lowering clouds.
2. 60-80 feet in 3 hours – consider bailing on summit bid
3. More than 80 feet in 3 hours – head for the cars!
4. 1000 feet over night gain at base camp – middle of a SERIOUS storm.
If the barometer/altimeter watch was not staionary, and you were hiking up and down with it, you would probably experience a pressure altitude change of more than 80 feet (about 2.963mb) in 3 hours, unless you hike slow as a snail, or are in one of those 'fly over' states which is flat as a frypan. Remember the rule of thumb that 1mb of mercury is equivalent to an altitude change of 27 feet (true at sea level). Your watch does not know "why" the pressure is changing.. And if the weather was getting worse, but you were hiking downhill at a certain rate, the alarm wouldn't warn you anyway!
What you are looking for CAN be found in marine units. All marine units operate at a fairly constant geopotential altitude (0 feet Mean Sea Level plus or minus waves, tidal surge, etc, in the oceans) therefore all barometric changes they sense are due to weather change, and such an alarm would have more validity.
Here is just such a marine unit, costs about $100 and uses 2 AAA batteries:
"Alarm feature to signal abrupt changes in pressure"
http://www.brandsplace.com/0026-4000.html
I have avoided discussing another wrinkle in this subject, which really throws wrist altimeters for a loop; non ISA standard pressure lapse rates and non ISA temperature. Subject for another post, but for now… here's a quick test for all you altimeter owners; calibrate so your unit shows the true altitude, and toss your device in the freezer for about 10 minuntes.. did the indicated altitude change? Is this good or bad, and why?? Anyone care??
