Motion Sensors
Motion sensors pickup where standard contacts leave off. In essence a motion sensor also contains a switch that activates when the unit detects motion. It is wired much the same as a standard contact is. Most include no and nc connections. In addition to contacts a motion sensor also requires power. A typical motion sensor requires 4 wires, 2 for zone connections, and 2 for power. When wiring power, be sure that you observe the correct polarity! The terminals will be marked "-" and "+" and should attach to the corresponding connections on the panel. Most panels have connections designed specifically for this purpose.
Motion wiring block
Many motion detectors include a "tamper" connection that opens when the cover of the sensor is removed. These should be connected to a 24 hour "supervisory loop" if your panel supports it. It allow you to determine if the motion sensor was tampered with while the alarm was off or unarmed.
The panel may have a power limitation that can limit the number of these types of devices you can attach. The manual will probably give you a total source power in "amps". If you add up all of your power drawing sensors, that number should not exceed the maximum capability of the panel. This is rarely a concern. Most panels are designed to accommodate many sensors.
Typical motion detector
There are several types of motion sensors. The most common is "infrared". Infrared (IR) is the type of energy that the sensor "sees". Humans (and animals) emit infrared energy and that is what the sensor looks for, changes in the infrared spectrum of the area it is pointed at. You should also note that infrared energy is emitted by appliances and typically anything generates heat! That includes your refrigerator! You must be careful when planning and installing IR sensors. Pointing it at the wrong part of the room can cause false alarms that are difficult to track down. A little testing will go a long way. More on this later.
Many detectors also include a "pulse count" switch or jumper. This can be used in troublesome areas and basically sets the number of "motions" the detector must see within a short period before the alarm is tripped. Typical selections are 1 or 2. Any real movement will typically be detected multiple times in a large area. Detectors can also be adjusted for "viewing" angles. This determines what the detector "sees". Consult the detector manual for more info. Most detectors also include a LED (light) that can be seen from the front of the sensor. It illuminates whenever motion is sensed. This is your primary testing tool! Make sure you do all testing with the lens installed! Without the lens the detector will probably not function at all. As an option, you can disable the the LED after testing on most sensors.
Microwave motion sensors work on a different principal. They emit a weak signal and measure the reflection (oversimplified). If the reflected signal changes, due to a new object in it's path, it closes a contact. Microwave sensors are now subject to false alarms by heat sources, but are subject to false alarms by other devices operating in the microwave band (to many to list). Because of the many potential sources they are rarely used alone.
Hybrid motion sensors typically combine a IR sensor and a microwave sensor in one unit. Both must detect movement before the alarm is tripped. These are some of the most reliable (least false alarms) but are also more expensive. These hybrids are also the best choice for outdoor applications.
You will also see references to "pet immune" detectors that are supposed to ignore motion by pets. The sensors have a modified lens and or modified electronics designed to ignore changes below a certain threshold. Others simply "cut-off" the detection range below a certain height. My personal experience with these has been spotty. Use at your own risk!