which relay to use with sensor?

Probably better with bandpass filters than freq switches, though I think the LM2917 frequency top voltage chip could be used as a window trigger... But as KP & Howard imply, it's a bit more complicated than that (needs some intelligent processing). And the alarm(s) should be isolatable. People have fun with systems that wake up the occupants or neighborhood. Proximity lighting is usually adequate.

Thankyou for the replies when i get the kit i will test it and be back Thanks oldspark i have a remote control fob to turn it on and off The proximity lights should as you say act as a warning but if they just light up the area for someone then the siren should send them running. As the proximty lights wont tell me anything if im sleeping but the siren should. Thanks Tony

Probably much easier to wire the proximity lights to a siren.

Ok the sensor and main control box and buzzer arrived today they are called Gadgetman parking sensor I tested the sensor first connected to the main box with the buzzer connected and as you move closer it has a quicker buzz .The manual says stage 1 150-100cm bi...bi...bi stage 2 90-50cm   bi..bi..bi stage 3 40-30cm   bi.bi.bi stage 4 0-20cm   bi............ I took out the connector for the buzzer that goes to the main box and tested the voltage I get a variable voltage upto a max of 6 volts for stage 1 to 3 and a constant 12 volts at stage 4 So is it a case of somehow spliting these two voltages so i can set the lights flashing then the siren Do relays or is there something different that will can trigger within a set voltage range. As you can tell im confused how to progress i search for the programmable frequency switch bit could not find one on the net Thanks Tony..

Thankyou for the reply I think im going to simply install led lights to the buzzer wire to have proximity lights. The siren does come on at the constant to start with but then turns it self off and back on at the pulse distance. I think to get it working how i want its more to do with having a new crcuit bord made,more to do with electronic`s than relays Thanks for all your help.

I love this idea! OP are you still arround and if so, did you finish this system? does anyone know where to get only the sensors themselves to experiment with? I'd like to create a two zones arround the RV where it first turns on exterior lighting then activates an audible alarm (inside the RV to alert or wake the occupants) thanks

DEI 508d or any quality dual zone proximity detector.