I recently bought my first laser pointer over 5mW and it's a 500mW one. I knew that even an indirect hit with the laser light can seriously damage your eyes, so I figured I would use my polarized Oakleys to protect my eye. Thank goodness I read a disclaimer somewhere saying that any glasses made for sun protection don't protect your eyes or I might have learned that the hard way. (I did buy some laser safety goggles) I was wondering what keeps sunglasses from protecting your eyes from lasers and what's the difference between them and laser safety goggles. Thanks!
Voltage source-Resistor-Doorknob(open) This is as simple a circuit as I can think of. Basically, once the doorknob is turned, the circuit is closed, current flows, and the alarm goes off. The resistor is simply a current regulator. For more intricate alarms, I can see the circuit using a transistor as a gate which regulates current flow. Some doorknob alarms use the principle of the electromagnetic field to trigger and alarm. Basically when the knob is turned, the magnetic field changes thus causing a change in current which sets off an alarm.
FBI agents don't sit and drink and play games on their cell phones while parked in plain sight in front of your house. If you are concerned, call the police and tell them. They can send a car around to ask the person what they are doing there.
