Radio signal interference
Any wireless device can be a source of interference for other nearby devices.
Ex. Microwave ovens, elevator motors, photocopiers, cordless telephones.
Bluetooth, WLAN 802.11b/g/n and ZigBee devices can all operate in the same radio frequency, leading to interference between them.
Solution: locate source of interference and eliminate it
Example: moving a photocopier or microwave oven to another room.