circuit that watches for phone ring and resets external device

Connect a 2uF, 250V capacitor in series with the ac inputs of a bridge rectifier and connect this arrangement across the telephone line. The

+ve output from the rectifier connects to MT2 of a suitable TRIAC (I used a BTA04-600) and MT1 connects to one side of a relay coil (I used a DIL 48V dc relay with coil R = 7800 ohms). The other side of the coil connects to the -ve terminal on the bridge rectifier. Across the coil connect a 220uF 63V electrolytic with appropriate polarity. A bi-directional trigger diode (I used a DB3) connects between MT1 and G of the TRIAC. Works like a charm.