ZigBee is designed for wireless controls and sensors.  It could be built into just about anything you have around your home or office, including lights, switches, doors and appliances.  These devices can then interact without wires, and you can control them all . . . from a remote control or even your mobile phone.
Although ZigBee's underlying radio-communication technology isn't revolutionary, it goes well beyond single-purpose wireless devices, such as garage door openers and "The Clapper" that turns light on and off.  It allows wireless two-way communications between lights and switches, thermostats and furnaces, hotel-room air-conditioners and the front desk, and central command posts.  It travels across greater distances and handles many sensors that can be linked to perform different tasks.   Figure 1 below gives a great example of how ZigBee can be applied.

Figure 1. ZigBee Application [16].
 

ZigBee works well because it aims low.  Controls and sensors don't need to send and receive much data. ZigBee has been designed to transmit slowly.  It has a data rate of 250kbps (kilobits per second), pitiful compared with Wi-Fi, which is hitting throughput of 20Mbps or more.  But because ZigBee transmits slowly, it doesn't need much power, so batteries will last up to 10 years.  Because ZigBee consumes very little power, a sensor and transmitter that reports whether a door is open or closed, for example, can run for up to five years on a single double-A battery.  Also, operators are much happier about adding ZigBee to their phones than faster technologies such as Wi-Fi; therefore, the phone will be able to act as a remote control for all the ZigBee devices it encounters.