There’s novel recent research on City Marathon Active Timing System Using Bluetooth Low Energy Technology by Chun-I Sun, Jung-Tang Huang, Shih-Chi Weng and Meng-Fan Chien of Taiwan.
The authors discuss the use of beacons vs RFID and create a system using Received Signal Strength Indicator RSSI and gateways connected to detector mats:
Beacons are carried by athletes. The gateways sync their times via NTP and send data up to a MongoDB database:
An accuracy of ±156 ms was achieved which compares well to the nearest second used to generally record times and resolution accuracy of 0.1s for commercial transponder timing systems.