Not much to tell here as the circuit speaks for itself. *The 555 can be a LM, NE, or MC(cmos) type, they are all pin-compatible. **C1/C2's working voltage should be increased to 25V if you decide to go with a 12V power source. Rule of thumb: the working voltage of capacitors are at least double the supplied voltage, in other words, if the powersource is 9Volt, your capacitor(s) is at least 18V. Transistor T1 can be any approximate substitute. ***Use any suitable relay for your project and if you're not tight on space, use any size. I've build this particular circuit to prevent students from fiddling with the security cameras in computer labs at the University I am employed. I made sure the metal casing was not grounded. But as the schematic shows you can basically hook it up to any type of metal surface. I used a 12-vdc power source. Use any suitable relay to handle your requirements. A 'RESET' switch (Normally Closed) can be added between pin 1 of the 555 (U1) and ground.
ne osjetljivost.. kad bi ga spojio na bicikal bi bio stalno aktivan jer se signal gubi u kosturu.. treba signal pojacat, a ako smanjim R3 pojacat cu signal (bar tako mislim), ali ce se smanjit osjetljivost
ne gubi se nikakav signal u ramu bicikla.
pin 2 je ulazni pin(triger) koji reaguje kad napon na njemu padne ispod 1/3 napona napajanja.
mogao bi povecati otpornik od 10M pa ce i osetljivost biti veca
mozda ti svira zato sto ti je bicikli dodirivao nekim metalnim delom zemlju, ili si zakacio minus sa baterije na ream bicikla...
ako nije nista od navedenog onda samo treba smanjiti vrednost otpornika od 10M...
pa nek' neko proba dirati 
nema gnd na njemu
Osetljivos da pojacas ili nesto drugo 
