That will scare the heck outta someone BUT if you want to remain low key a small can or something that will make a slight noise would be better. That way if someone hits it you will have time to set up an ambush or slink away
Fishing line or bailing wire strung between knee and ankle height around your perimeter. Use spaghetti o sized cans, do not completely remove the lids leave the lid attached by about 1/2" of metal. Bend the lid over outside the can to form a hook and hang your can over the wire. Place 3 or 4 marble sized pebbles on each can. when something runs into the trip wire it will rattle. The drawback is you need hundreds of feet to encircle a decent sized perimeter and then someone has to stand watch to listen for it. The arny used this method in Vietnam to cover likely avenues of approach not entire perimeters and even then a perimeter for an infantry unit on patrol maintained 50% security (1 man awake and 1 man sleeping per foxhole). More permanent firebases used trip flares. Get a good dog.
yep, we used to do the can thing all the time in my Army days, but someone has to be on the OP/LP to hear them, sometime they are quite faint. in a housing scenerio the shotshell would work but you are right they are loud. a shotgun signal flare would also work, but you run the risk of setting someones roof on fire, big liability now, but when the zombies come....i agree with the dog...i have 3
oh crap i have this in my house and i forgot all about it. it's a driveway alert! the infrared beam goes across by foyer about 15 feet from the front door, when it is broken there is a unit on top of my fridge that beeps really loud 3 times. you can turn it low or high. scares the crap out of me when a big moth or something breaks the beam. duh i forgot all about that thing! you can also get the pressure mats that gas stations used to have and rig to a bell. my favorite book had one of those rigged to a bell and also rigged to a clock that activated when it was tripped. that way you could see exactly how much time had expired when said alarm was tripped.