The following diagram depicts a circuit intended for activation via reed switches. Q1 is normally conducting through the voltage divider R1 and R2. With Q1 conducting, Q2 is biased off (non-conducting) via R3 and R4. The SCR remains non-conducting. When the magnetic reed switch opens, Q1 no longer conducts, after which C1 discharges into the base of Q2 via R3, which causes Q2 to conduct. The SCR receives current through C1,R5 and R6 and it activates the relay. I'd like to know whether this circuit benefits from filtering components, considering the reed switches (window contacts) are connected via long wires to the circuit and might need components to remove RF and other sources that might induce noise into the circuit.
I was thinking of adding a reverse diode (or TVS) before the first voltage divider. Also, adding 100nF cap at base of Q1. Please share your suggestions.