Poachers carrying a phone can be detected, triangulated and in effect: rangers will be alerted.
Detecting phones is one of the most wanted features by conservation parties and rangers because poachers heavily rely on their mobile phone for navigation and communication. It is one of their most important tools. Phones are used for communication with other poachers to come help extract the ivory. In general, a poaching operation consists of a team that needs to communicate together.
"The poaching of rhinos in this 300,000 hectare area has been widespread – both in the peripheral area and the central area. So we are working on building up manpower, but that takes time. All these poachers made use of cellphones. Two poachers were recently arrested and two were killed after they crashed their car while they were trying to escape after cellphone-coordinated pickup on the boundary of the conservancy.
If we had GSM detectors we would definitely have detected them."
— National Park Ranger - Deliberately anonymous, for security reasons