How do you spot a hidden motor in a bike frame? Did the UCI use magnetic fields?

One of the interesting debates in the mechanical doping scandal that has enveloped the cycling world for the past week has not been that the UCI found a hidden motor, but exactly how it found the hidden motor. 

The UCI has been conducting random tests for hidden motors for the past few years, but this previously required some dismantling of the bike to see if there was a motor in the bottom bracket or seat tube. That's not very convenient or easy to do.

- Mechanical doping: All you need to know about concealed motors 

This isn’t how the hidden motor in Femke Van Den Driessche’s bike was found at the weekend. Instead, the UCI apparently used an app on a tablet to detect the hidden motor. It's reported to be able to quickly and easily scan a bike for a hidden motor. 

Precisely how this detection system works is unknown. The UCI hasn’t provided any details. And it likely won’t, in an attempt to stay one step ahead of anyone wanting to commit a mechanical fraud, as the UCI calls it. 

Wired magazine has explored some of the likely detection systems that the UCI might have used to find the hidden motor, though. It concludes that a magnetic field detection should work because it doesn’t need an additional device and works with a simple app. Modern smartphones have a  magnetometer sensor - that’s how the compass works, and it’s used by mapping apps.

- All our mechanical doping coverage here

And that's what could be used by the UCI. Motors work with magnets, a coil and a battery, and magnets produce magnetic fields. Wired magazine reckons a readily available app could be used on a tablet to detect a magnet in a hidden motor, with no additional devices needed, and the motor doesn’t even need to be switched on.

Liverpool University, in an article on using a smartphone to detect shipwrecks, says a simple smartphone app can be used to “evaluate the total magnetic field strength” simply by placing the phone over an electric motor and looking for a change in the reading of the magnetic field.

Here's a video that demonstrates how it works:

Wired also explores other possible detection methods, which have their merits but don’t look as plausible as the magnetic theory. 

Infrared Imaging, using an infrared camera attached to a tablet, can detect the radiation given off by hotter objects, such as a hot motor. That would only work if the motor was in use, or had been used recently, says Wired, which might rule out its effectiveness. The bike that was detained by the UCI hadn’t been ridden so it’s likely the hidden motor wouldn’t have provided a heat signature. 

The other option, says Wired, could be detecting the radio frequency electromagnetic radiation between the handlebar mounted controller and the motor if there were no wires running through the frame. The motor could also produce radio waves but Wired says that some sort of separate device plugged into the tablet would be needed, and it rules out this option. 

So magnets look like the most likely option, and the UCI is using nothing other than the magnetic fields produced by the magnets in a motor and an app on a tablet (or smartphone) to detect the hidden motor. 

Wired also looks at how much run time could be achieved with a battery concealed inside the bicycle frame and concludes 16 minutes with a 200 Watt motor. That doesn’t sound like much, but if used in short bursts, as it surely would in a cyclocross race, could be just enough to provide a performance benefit.