We use an older model of this device (been running for 3 or 4 years, I 
think):

http://www.sensatronics.com/products_temperature_model_e.html

Sensatronics (formerly TempTrax) also sell devices that monitor 
humidity, etc.


It's embedded Linux and serves the temperature as a web page and XML 
(not USB as you originally asked).


It is handy that when your alert goes off you can http right to the 
device to see the real temperature.  To automate monitoring, you'd just 
need to parse the html or XML output.  We actually use IPSentry 
(Windows-only) software to monitor the device.


These devices allow multiple probes so we put one right at the AC vent 
and one near the rack.  We know immediately when the chiller stops 
blowing air at 68 degrees and also know when the rack itself is getting 
dangerously warm.


- Dan



Brian Bartholomew wrote:
> Occasionally the chilled water goes out in my machine room/closet.
> Today I have an old Sun with an internal air temp device that sends my
> pager mail.  I'd like to decommission that Sun, and replace the air
> temp monitoring function with something else.
> 
> I have not been successful getting lm_sensors working under several
> versions of Linux.
> 
> Does anyone know of an inexpensive external temperature sensor with a
> USB interface?  Stuff comes up on google, but I'd prefer to know of a
> model that's inexpensive and already seen to work.
> 
> 							Brian
>