PREMISE: Defending an area (especially bases) can be tricky if the enemy has a lot of places to hide on the approach. Also, one cannot be looking everywhere all the time and expending troops on simple patrol missions limits the numbers which can actually go out and engage the enemy. To solve these problems, alarms and watermines can be set-up around an area of interest to hit enemy troops moving in the area or alert one if the enemy is near.
ALARMS: The best and cheapest type of alarms to use are based on the tripwire. However, instead of being a tripping device, the trip-wire alarm is designed to make noise when crossed. Fishing line or black thread work best since they are hard to see. The line should be supported about 4" - 6" above the ground by sticks or some other hard-to-notice means. The line is fixed at one end and attached to a noise maker (i.e. a bell, some sticks & cans, personal alarm) at the other end such that if the line is pulled, sound is made which can be heard at least 30'-50' away to provide a good forewarning signal.
Just be sure to note where the alarms are set in order to not activate them, oneself.
WATERMINES: Watermines are devices which are designed to fire water at the enemy upon being stepped on. Watermines are based on empty soft, plastic bottles. Larger (not too large) and softer the bottles work better since they hold more water and fire more water quickly.
To make a water mine, start by making sure the bottle is empty and rinsed well with water to get rid of the soap, shampoo, etc. which it had previously contained. Note: Do NOT use any bottles which had contained toxic substances such as bleach, toilet bowl cleaners, etc. Once cleaned, first fill the bottle with water, fasten the cap and make sure there are no leaks by gently squeezing the bottle. If no water comes out, empty the water and drill/make two holes into the bottle on one face: one near the top and one near the bottom. The holes should be about 2mm in diameter. If the holes are too large, range is reduced. If they are too small, not enough water will be fired. Two holes are suggested so that if one is covered when the device is stepped on, the other will still fire. Once drilled, fill the bottle by opening the top cap, holding a finger to close the bottom hole, topping up with water, then closing the top cap.
Mines should be placed hole-side up in shallow holes around an area of interest and camouflaged using some leaves or a very thin layer of soil.
PLACING TRAPS: Booby-traps and alarms are best used to defend a base. Watermines can also be used to fence in the enemy, but this can be tricky and require many more of these devices and time to set-up.
The above diagram shows a suggested pattern of placement for alarms and watermines. Alarms should be positioned a little farther from the base to give a good notice-time when the enemy is approaching. Watermines are used to guard the base entrances to soak any enemy who tries to enter.