there's what moonshiners use.which is string/twine or wire with cans or what ever attached to them..seeing how that makes plenty of noise.then there's the silent alarms.a electronic divice set up out side and away from the home.and it alerts the part in the home.and in return it alerts you..but that can be a problem with no electric..pets if taught n trained properly..even a talking bird of some breed might work..
There are so many options all based on proximity and common sense. I use distant ones with a rat trap tripping off a twelve gauge shotgun (no pellets) shell for distant noise. As things move in to an area of fire, I use a flare system especially since I use night vision scopes. Anything closer are quieter proximity alarms until the nearest alarms are silent to me only. All very easy to make if you search the web. All distant ones are trip wire so u don't have to travel to replace batteries, etc!
Depends, do you want a trap type trip wire, or just for alerting? You'll hear a dog barking much further than cans rattling. Personally, I use that option, but I'd also like to get some solar powered driveway alerts, etc.
Get your hands on a copy of the DOD's Improvised Munitions Handbook. It teaches improvised weaponry and you can adapt many of the triggering devices to your needs. Also, theres an old book called "Deadfalls and Snares" that I picked up a while ago that is really helpful too. Good luck.
If a warning alarm, one of the best options is to take one of those battery operated door/window alarms, where they magnetically connect, and then have it to where the trip wire would disengage these, resulting in a loud, piercing alarm. Make sure you use strong wire though, because you don't want it to break, just to give a bit, enough to separate the trigger piece. (plus, this is pretty easy to reset).