I think the alarm that CALM mentioned is the High/Low alarm. I've got a Herpstat 2, and it's great.
The alarms only trigger at temps you set them to (and it is definitely not talking; just beeps). So if you set it to heat to 90 degrees, you can set an alarm above and below that number by whatever amount you're comfortable with. For example, if the temperature is set at 90, you can make alarms for 85 and 95 degrees. That way, if the probe is sensing above 95 or below 85, it will start beeping to alert you something is wrong. The threshold temperatures are set independently, so one could be 92 and one could be 87, or whatever you want.
I haven't used it, but I think there is another option you can enable that makes the beeping quit after 30 minutes, even if it is outside your "OK" range (85-95). (I just let mine beep indefinitely because it means I need to do something and fix it.) Not sure exactly how it works.
For me personally, I find that +/- 3 degrees gives enough leeway the fluctuations caused by the increasing/decreasing heat and (for an RHP cage) for the temp changes from opening the cage for short times. I've only had alarms trigger so far when doing bigger cleaning where the RHP cage was opened for an extended period or when I pulled a tub off of the heat tape and had an exposed probe get too cool in the room.