[SOSCEO]

I use a couple of these things around my house so I can tell if someone comes in the driveway. The ones I use have a range of 200-300 feet, are waterproof, and the battery lasts well over a year. By themselves, they do nothing but transmit a radio signal when motion is detected.

All a terrorist would need is to have the receiver in a bag or suitcase wired to trigger some type of explosive and boom! They could carry the bag onto the train 500 miles from the trigger point, and ride safely and get off at some point in between, leaving the bag on the train.

This could be done at a time of their choosing, today, tomorrow, or 6 months from now. Once the trigger (sensor) is in place, all they need to do is to get the bag on the train. When the train goes by, it triggers the sensor and if the bag with the receiver is within range, that's all she wrote.

What worries me is that there are very high quality, reliable electronics (much better than X-10) available for $200 or less, and sensors like these could be put in place months in advance.

[oceanview]

why bother with all that when a cell phone call can be used to detonate the device on the train? why risk going out to the tracks to plant a device? they could also trigger it by being in a car near the tracks, on an overpass or something, and using a handheld garage door opener to trigger it as the train passed by.

[dinasour]

I use a couple of these things around my house

So do I. They work quite well. And would definitely be triggered by a train passing.

This is scary. I can't think of a darned reason why someone would do this, other than to trigger something.