If you have an aftermarket alarm you can easily tie it into your alarm. All aftermarker alarms have a circuit that turns to ground when the alarm is armed, it's what is used for a starter kill relay. Just simply wire your radio to a constant hot wire for both power wires on the radio. Run the wire that is normally the ignition switched wire through a SPDT bosch relay using the ground output from your alarm to control the relay. When you arm your alarm with radio will turn off, when you disarm your alarm the radio will come back on.
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