This is the enemy. This is FRED This blinking black box replaced the caboose on the rear end of the vast majority of freight trains in North America.
FRED is an acronym of Flashing Rear End Device. it is also known as End Of Train Device or EOT for short.
FRED simply monitors main brake line pressure, relays that data back to the engineer in the lead locomotive's cab. Some FREDs can remotely apply the brakes using a signal from the engineer in the lead loco.
Most railfans hate this little box. So do I.