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RE: Question re: Radio security codes

>Many auto parts stores sell a device which plugs into your cigarette
>lighter adapter.  It contains a 9 volt battery.  This device will provide 
>enough power to your radio so it keeps is memory.  The electronic clock in 
>your car also will keep the time.

I've built it myself and... threw it away.
The problem was in my alarm. I have a Prestige APS200 with all the good 
stuff. Most alarms have an anti-battery-disconnect mode, they go off if 
someone tries to disconnect the battery and to reconnect it again. What 
happens is that a car drains 30 to 50ma just to run the memories (radio, 
ECU, alarm itself etc.). When you disconnect the car battery the tiny 9v 
battery drains and drops it's voltage. When it reaches a cirtain pre-set 
level the alarm's brain thinks the main batt got disconnected. Then even a 
slightest fluctuation above that treshold would fool it into thinking that 
there is a theft attempt in progress. It will set the siren screaming. 
Well, since the batt is only 9v and falling, it will sound more like a cat 
who got his tail stepped at. A cat with a flu that is.

I was laying under my car draining the tranny, when it happened. You should 
have seen me jumping around and leaking oil off my fingers and cursing on 
three languages. I thought it was the smoke detector above. The most trouble
was to understand that the noise was coming from a car without the battery.
You know how a piezo siren sounds like in a garage with the closed gate!
Actually, when I come to think about it - that was hillarious.

Don't get me wrong-the device is a big help. If you don't have an 
aftermarket alarm installed...