There are many other forms of sensing devices we haven't talked about in this chapter, including various gas sensors, humidity sensors, radon and radiation sensors, smoke sensors, ultrasonic sensors, and so on. This chapter, however, should give the reader a working knowledge of the sensor input fundamentals and challenges in choosing the correct sensing options.

Up to this point, we have discussed endpoint devices such as sensors. These devices send a constant stream of data to an edge device, or the cloud. The IoT consists of bi-directional systems. Input may arrive at an endpoint from the cloud, or data may be sent from an endpoint to multiple subscribers in the cloud. This short section covers basic actuators and output devices.