Originally Posted by ala_xfire

SKREEM = Sentry Key Remote Entry Module
Your key fob has a non powered 'chip' in it, when the ignition is turned on the SKREEM causes the halo key ring antenna to excite it, then monitors the frequency generated.
If the frequency is correct the SKREEM signals the PCM ( Powertrain Control Module ) that all is well and it may proceed with the complete start procedure.