DG81781: RailBAM (Bearing Acoustic Monitor) equipment installed near Swaythling. This has an array of 16 microphones that can listen to a passing train and identify whether the axle bearings are sounding normal or making a different sound which might indicate the onset of failure in the future. Manufactured by Trackside Intelligence and installed by Siemens, the RailBAM product installed in the UK is a European first and the first to be employed to monitor passenger vehicles.

Here's the equipment at rest with the hatch closed to protect the microphones from the elements.