BA allow 2 pieces of hand luggage, this would be one of them. You can check devices with Li batteries which are fitted to the device.
I was wondering same for a trip with BA (grrr…) in June.
The helmets have comms so presumably lithium batteries and would need to be hand luggage. For me question would be is this in addition to hand luggage allowance as does it use the allowance and I have to stuff things inside of it ?!