2002 trailblazer door lock sensor

Key fob needs to be within 10 feet to lock doors. New battery in fob. sensor ?

Sounds like the sensor. You can probably pick one up here (http://www.gmpartsonline.net/2002-chevrolet-trailblazer.html) if that is indeed what it is. You also might want to try another fob if you can.

Stick fob under the chin, and press the button...see if range increases.....