I'll try to keep this concise. I am trying to build a alarm system for the DAQ system in my lab that will be software (LabVIEW) based and will replace the current hardware tripped alarms. Right now I am working on a final fail-safe alarm to protect against the freezing of the "alarm server" computer which sets off a telephone alarm (Sensaphone Express II) via a USB DAQ. As a mechanical engineer I'm not all that familiar with all the IC components available, and my electronics technician is more or less brand new. If the computer freezes, the USB DAQ will also freeze in whatever state it is in. To make this an alarm condition, my first thought was to have a digital counter that would count to some threshold at which it would set off an alarm (currently an alarm is triggered by the signal changing from 5V to 0V). The USB DAQ could then send a reset signal every so often, so if the computer or DAQ froze the reset signal would not be sent and the counter would trip the alarm. My technician also had the idea of using an IC, I believe it was an LM555, which she explained could accept a pulsed signal and if it went outside the determined frequency, it could change its output from 5V to 0V, thus tripping the alarm. Does anyone here have any suggestions or criticisms for either of these methods? Hopefully this makes some sense to you. Thanks for bearing with me.