Resetting 555 via Transistor (optionally driven by Touchplate/Piezo)
You need a limiting resistor for the transistor, otherwise it will source a large amount of current and burn out. This is just an example circuit below, size the current limiter to the value appropriate to your circuit

You are seeing 50Hz because you have not isolated your test setup from AC mains 







simulate this circuit &ndash; Schematic created using CircuitLab