I have been thinking about installing a driveway alert system for my new house as my driveway is 100 yards long and I don't know someone is coming until they are literally in my front yard. I went on E-slay just to see what is out there. The typical "as seen on TV 19.95" junk is prevelent, however, there are a couple vendors that claim to build their stuff to Mil-spec. It was interesting in that the high dollar items allow you to put up to four sensors on one alarm. Got me a thinking. What if one was to get all four and put them out in the woods surrounding the house. That way, some meth cooker has a couple of hours to burn and wants to walk up around your property while is cook is cooling, viola' instant intrusion detection device!!! I know it violates the basic rule of no batteries for SHTF, but until they die, you have a instant protection system. With a solar recharger and some lithium batteries, you could be set. What I don't know is how long the batteries normally last.