The short-range sensor module is ideal for Millibots that have to work in tight or cluttered areas. The long-range sensors are more effective in environments that are more open such as hallways or open office spaces. Because of the size of the sonar detector compared to the robot, Millibots can support only one sonar unit per robot. For some tasks, it may be desirable to have both short and long-range sonar sensing available. A potential complication with sonar sensors is the interference with sonar modules on other robots.
Most sonar elements operate at a fixed frequency determined by their mechanical construction.
Therefore, two robots using ultrasonic sensors in the same area may cause interference for each other. To provide continuous rudimentary obstacle detection, a Millibot may opt to carry an infrared proximity module. The proximity module provides an array of five infrared emitter-detector pairs that trigger when an obstacle intrudes within its cone of emission. The proximity elements can be calibrated to provide readings of up to 0.25m. Although the proximity detectors cannot be reliably used for range determination of objects, they can be used very effectively in conjunction with a sonar detector module.