Calling a laser a “trip wire” is not exactly grammatically correct, since it is not, in fact, a wire, or even solid, but the metaphor works since the overarching purpose can be the same: detecting and/or preventing the intrusion of unwanted company.
The folks at Liquidware custom-rigged a laser-based alarm system as a response to how the $100 million Perimeter Intrusion Detection System from the JFK International Airport was undermined by a jet skier that, after an incident at sea, had to swim to shore and got on the tracks by climbing over the fence facing the waterside.
The idea behind the invention is simple: a laser pointer beam is projected through an aquarium and captured by an Arduino light sensor.
When anything interferes with the beam, such as a toy shark, an alert is sent to an Android-running BeagleBoard xM, which then sends a twitter message to the proper authorities.
Obviously, this isn't going to start catching scuba-diving infiltration teams any time soon, especially since the small scale of the “trip wire” makes it useless for anything short of fun demonstrations.
Nevertheless, the idea itself has merit and should be easy enough to implement across a larger area, especially if more powerful sensors are used.
In fact, rather than airport security systems, the invention could be used to catch real sharks, perhaps notify when such fish come too close to areas where people are swimming.
“Making this work on real sharks would require: a powerful, underwater stationary laser beam, a receiving photosensor, and a finite distance of water through which the laser would be known to penetrate,” says Liquidware's Justin Huynh.
“How far the laser could go would depend on the opacity/diffusion of the water, and you could tune the sensors to go off only if blocked for greater than a certain amount of time, to avoid picking up small fish. It would probably would work better in clear shallow waters than the deep blue sea.”