what's wrong with my gas water heater?
Theoretically as long as the gauge indicates it is fully charged it should be OK. Here's the deal; the product inside is a powder and it can compact and compress over time so even if there is enough pressure in the canister the product won't come out. Pick up the canister and turn it upside down and then right side up in a shaking motion. Can you hear/feel the powder shaking around loose in there? If so, between that and the pressure gauge it is still useable. If you can't feel anything moving around in there then you would do well to replace it. Hint: If it is still good you should shake it up at least once every two months or so to keep the powder inside from compacting. Fire extinguishers have gotten pretty expensive and it's worth the effort to keep them good as long as possible.
I think it depends on how new, and advanced the alarm is but i know the new ones will squirt ink out ive seen it happen 3