Donzilla.com

Arrgh! The Sony DSXS210 has no option to disable the “caution alarm” that sounds just after the car is turned off… A few of their 2011 models are similarily crippled. The one loophole is that if the head unit is plugged into an external amp, that noise won’t sound through the speakers. But one of the admirable things about the head unit is that it has a great amp in it!

http://esupport.sony.com/US/p/model-home.pl?mdl=DSXS210X&LOC=3&session_id=e932fba7a49e57a5fe734c7ea812f570#/howtoTab