I'm wiring a 12V home alarm system: magnetic door contact triggers lights/sirens...but when burglar closes door, I don't want sirens to stop - just continue until I hit a toggle switch that breaks the circuit. What would be best for that situation? SCR? Latching relay? Input to the SCR gate or latching relay would only be about 2.2V (powering an LED indicator light along the "gate" circuit so resistor will have to power it down to around 2.2V), but I'd need the SCR/relay to run a full 12V through it to power the sirens/lights. My concern with SCR is the gate being too sensitive that it may accidentally trigger from a power surge. My concern with a latching relay is I can only find two types: single or dual coil. Don't like that because I don't want to have to reverse polarity (single coil) or apply separate voltage to a reset coil (dual) to return it to default state - I just want it to "spring" back to open state when I kill the whole system. Any ideas?