This is the Directed 506T Glass Break Sensor.

Enhance the security of any install with an optional audio sensor, which detects tampering and breaking of the vehicle’s glass using a microphone and a microprocessor, which analyzes the frequency, intensity and timing of intrusion sounds to eliminate false alarms. Detects even “soft breaks” where the glass is shattered quietly, which might not trigger the shock sensor. The 506T adds an additional layer of protection.