No need to take apart thermometers. Every Walmart and hardware store
carries small digital
thermometers that have an "outside" wired sensor for less than $10.
Put the sensor in your vent
and stick the little display anywhere. It never turns off either.

To get temperature into your Dell Streak use the IOIO box and a serial
output temp sensor.
Something like this:
http://www.microchip.com/paramcharts...branchID=90003