product request - Serial controlled relay

I am looking for alternates to a product, any vendors or manufacturers please post spec links and budget prices.

Product is a relay that will change state when a particular serial stream is received. The catch is that I will specify the stream the device has to listen for.

This device will be used to monitor serial communications between two other devices, and when command 1 is sent, the relay switches on. When command 2 is sent, or it has been more than 3 minutes since command 1 was sent, the relay switches off.

As this device is 'sniffing' an exising serial stream, it must receive in 3-wire RS232.

Thanks!