The Zone Protector is capable of detecting cell phones inside a 100 foot radius using its standard internal antenna.
However, the detection distance depends on the environment and surroundings e.g. pillars, concrete walls, distance from cellular towers etc.
(Similar to a Wi-Fi installation)
The Zone Protector's sensitivity settings can be adjusted to reduce the detection radius down to approximately 5 feet for installations that require detection within a specific area/zone