Lidl has rolled out its own "smart" bike helmet. It is competitively priced at £39.99 (as of April 2019) and features a rear light and indicator lights. The rear light can be either continuous or flashing, and all light controls are accessible from a remote control that fits onto the handlebar. From the picture on the box, the remote control doesn't appear to be terribly weather-proof, and I'd be surprised it it lasted more than six months of regular riding in UK weather!
The helmet itself is quite a basic affair and comes in just two sizes (S/M or M/L) with a ratchet mechanism at the back to get a snug fit. It is fairly light considering the extra electronics and battery that are packed into it. Actually, the battery is the elephant in the room here: we don't know what form it takes or how to recharge it. Definitely something to investigate before purchasing.
I cannot agree with Jules' comments that this is a "terrible product" just because the controller doesn't fit a road bike - it fits an MTB, all three of mine, so it is NOT "terrible", that's poor reviewing (sorry Jules!).
I love this helmet - had it probably 5 years now, my only complaint is that you can't tell when the battery has run out, which IS a major disadvantage if you're relying on it for your safety! That said, I always run two lights on the frame of my bike anyway, each just in case one runs out, I run the helmet light as a third, redundant safety.