FLEX is a communication protocol developed by Motorola and used in many pagers. FLEX provides one-way communication only (from the provider to the pager device), but a related protocol called ReFLEX provides two-way messaging.

Transmission is at 1600, 3200 or 6400 bits per second using FSK modulation. At 1600 this is on a 2 level FSK signal. The 3200 and 6400 have a symbol rate that is half of the bit rate and use a 4 level FSK signal.

Data is transmitted in a set of 128 frames that takes 4 minutes to complete. Each frame contains a sync followed by 10 data blocks. The data blocks contain 256, 512 or 1024 bits for 1600, 3200 or 6400 bits per second respectively.

A BCH type ECC is used to improve the integrity of the data. The standard has been designed to allow the pagers receiver to be turned of for a high percentage of the time and therefore save on [[Battery (electricity)|battery] usage.