Motion and light sensors
You don’t always want to have to push buttons — wireless or not — to make something happen. Instead, as with outdoor security lights, you may want to trigger actions based on light (or its absence) or motion. Motion sensors (Table 1-5) solve that problem, sending messages for both motion and light. The X-10 MS14A is a wireless motion and light sensor you combine with a wireless transceiver, while the wired PR511 combines outdoor lamps with a motion and light sensor.
Figure 14 shows a sample motion sensor application — controlling overhead lights in a garage.We placed three motion sensors, to make sure people were seen when they entered the space, and located the transceiver so there would be direct line of sight from the wireless motion sensors (we used X-10 MS14A sensors) to the transceiver. If you were to move the transceiver to an outlet directly above the metal shelves, for example, the path from the sensor on the bottom wall would be blocked and the sensor would operate only erratically, confusing the system when Off messages were dropped.
FIGURE 14: Motion sensors for automatic lamps