The security flaws on this common hotel keycard lock are nothing short of face-palmingly stupid. Look closely at the picture above. This is a hotel room door swinging open. The device he holds in h… ...

Essentially, each pnp transistor compares a reference voltage on the npn emitter with the voltage across the lower limit switch circuit resistors R4, 5 and 6, directing current to the led if the limit ...

To create the DIY remote shutter button, [NirL] used a spare limit switch, resistor, and cannibalized an old set of earbuds for the cable and 4-conductor 3.5 mm audio plug.