You probably already own the basics: screwdrivers, wrenches and an electric drill. In addition to these basic tools, you should have the following available:
A panel removal tool to get behind your dash and the other places you'll need to access.
A wire cutter/stripper. For many vehicles, plug-in interconnect harnesses simplify security system connections. But even if you use a harness, you still may need to splice some wires together.
Use heat-shrink tubing or electrical tape to protect your connections.
A wiring diagram, specifying sensor wire colors and functions, comes in handy and can usually be found via an internet search. If none can be found, you'll have to check each wire's function with a meter while activating the sensor.
Use a multimeter (voltmeter) to verify the functions of vehicle wires you splice into, or to determine what kinds of switches your vehicle has. You need to test the wire because car makers occasionally use different color wires than the ones specified on their wire color sheets.
DO NOT USE A TEST LIGHT instead of a multimeter. Test lights draw too much current and could damage sensitive circuits in your vehicle.