In March, 2003, researchers managed to cram all of the parts needed for a mote onto a single chip less than 3 millimeters on each side. The total size is about 5 square millimeters, meaning that you could fit more than a dozen of these chips onto a penny.
The chip contains all of the components found in a mote: a CPU, memory, an A/D converter for reading sensor data and a radio transmitter. To complete the package you attach the sensor(s), a battery and an antenna. The cost of the chip will be less than a dollar when it is mass produced. See this page for details.
For more information on motes, their applications and related topics, check out the links below.