Hardware for automated sip dialing

I’m looking for SIP hardware suggestions that would help us send automated alerts over our asterisk phone system. I have a paging group already setup that would receive the alerts. My alert source closes a relay and plays the automated message, then releases the relay when the message is complete. I’m looking for hardware that will…

  1. sense a relay closure
  2. dial the paging group when the relay is closed
  3. play the audio inputed into it from the source down the sip channel
  4. hang up when the relay opens

does anyone know of such a device/gateway/dialer etc?