This morning I was once again musing about things I know nothing about; in particular, laser-based intrusion detection systems. You know, the Bond-esque laser grids that let you know when someone's breaking in to steal your diamonds in that display case in the middle of the room. What I was wondering is simple: why can't these systems be defeated by some kind of portable light carried by the intruder?
Here's my scenario: I'm trying to steal the aforementioned massive diamond on display. I take with me a bag containing several devices which are essentially "flashlights" that produce light that the system would think was the laser, but they do so in a wide beam so that all of the sensors on one side of the case can be covered. I need one such flashlight for each side of the case that contains sensors. Once a steady stream of light is projected over all of the sensors, I could just reach in and take the diamond, and then turn off all of the flashlights and leave.
My first guess is that there's no portable way to generate the wavelengths of light that the sensors recognize in such a large area. Maybe laser light can't be diffused easily enough to create such a "flashlight" beam. Maybe those sensors are precisely calibrated to only recognize a very specific wavelength of light which wouldn't be known by the attacker ahead of time.
My second guess is that there's no way to trigger the sensors with diffuse light, and that it can only be done with tight beams projected directly at them, namely the lasers that are supposed to be part of the system.
If anyone knows why, please feel free to educate me.
Of course, if this were a vulnerability, there are several things you could do to protect your system from such attackers. The easiest thing to do would be to include at least one sensor that must not be receiving light to avoid triggering the alarm. The flashlight would hit this sensor along with the others and you'd be caught. The next step would be to cause all of the different lasers to turn on and off in a particular pattern, and then any sensor that didn't match the state of the laser assigned to it, either on or off, would trigger the alarm. That seems like it would be a really effective countermeasure.