Subchannel chip

From Wiki 24

A subchannel chip is designed to receive a specific signal which cannot be traced. Although not referenced to specifically after Day 3, it can be assumed that this is what makes phone signals untraceable in future settings.

[edit] Day 3

This was placed inside the phone that Stephen Saunders delivered to President David Palmer through a drop during Day 3 5:00am-6:00am. Secret Service Agent Aaron Pierce had several colleagues examine the phone to make sure it was clean. It was discovered that there was no threat but that the chip was built in so that any attempts to trace Saunders' call would be futile.