If you try to start it with out pressing the unlock remote button then turn the key nothing other than the dash lights dim out for a second like it will try to start but nothing happen starter does not even click.
When you turn it off to start it again you have to press the unlock button on the remote again to start it.
Weirdly I have been having issues with the trailblazer the alarm is original no modifications to the vehicle if this is not normal maybe the truck has a bad PCM been having weird codes popping up see this thread
https://gmtnation.com/forums/threads/05-trailblazer-bad-pcm-question.20373/ and you will see what I mean almost every thing under the hood is new and engine rebuild around 100 miles running out of parts to change.
Don't trust the vehicle until I debug it in town driving only.
Only new items I can change under the hood is the complete wiring harness, PCM, battery, AIR conditioner compressor and the mass air flow sensor meter on the hose between the air filter and throttle body. The intake map sensor is new the intake manifold is original I cleaned it out (de greaser and power washed it let it dry 3 days in the sun and replaced the hose on it made it like new has no cracks or leaks..
Look at my other post maybe I'm on the right track now knowing the press unlock button on the remote to start the trailblazer is not normal. Been working on this truck for a tear and love it but it's a bugger to work on gone to far to turn back now
My biggest worry changing the PCM is I now the security system will re sync with the key just left on for 30 minutes but finding a mechanic that can relearn the crankshaft position sensor to the new PCM in my area I know the chevy dealer will ask for my next child to do this.
unless there is a back boor procedure to program and relearn the crankshaft position sensor via turn key on or off pressing gas pedal down or some thing like that.
Your help is appreciated!