Product review (5 stars): 5 years and still going strong
I've had the Vick's humidity monitor for 5 years now and it's still running on it's original AAA battery.  I've used it in several places over the years including the nursery (overheating is linked to SIDs.)  My favorite use was to prove to my boss that my office was too hot.  Apparently my part of the office hangs out at 76 and humid when the thermostat in the other part of the office was set to 70, and Vick's said they had 70 too!  Love this and highly recommend it!