The 2 circular sensors are inside the apartment on the wall, above and off to either side of the front door. The rectangular thing is outside the apartment in the hallway above the door.
Circular sensors are probably less than an inch in diameter.
I love a lot about this scooter. The portable size, under 50lbs, easy maneuverability, top speed of 38kmph is good enough...however there's one major flaw that freaks me out.
My town is hilly and somewhat rural. We have a few punchy, rolling hills which aren't too long, maybe a few hundred metres, but they're steep enough in parts to cause the scooter to accelerate above its top speed. When this happens, the scooter seems to randomly (not consistently) engage regenerative braking at varying degrees of intensity to slow me down. It does this regardless of whether I'm using the throttle and brakes. It does this when regenerative braking is disabled. It does this usually for a split second, up to a second, then releases. If you aren't ready for it, it will throw you forward nearly over the handlebars or out of control if you're not anticipating it. Wen you're anticipating a casual cruise downhill with no surprises, it just does this.
Tonight, it surprised me more than usual. I was in sport mode which is rare for me as I usually rely on a custom mode to dampen acceleration and save power, but tonight I needed the power to get over some hills. On the way down a particularly steep but short hill, I released the throttle, didn't use the brakes and expected to coast. I saw my speed reach 47kmoh and then the scooter decided that was enough. It locked up the wheels causing me to skid briefly, then it locked up the wheels again causing another skid. Thankfully I'm not new to this scooter anymore and was crouched with a lower center if gravity and a strong grip on the bars and averted a total disaster.
I understand I was allowing my speed to build up higher than what Niu wants it going, but this is a potentially catastrophic way to control for this. In my circumstance, there was another uphill section immediately at the bottom which it would have been nice to have that speed leading into. It would have been nice if it could simply cap the accelerator at 38kmph and not metaphorically put sticks in my spokes during a steep 5 second acceleration on my commute.
Anyway, this scooter is a daily workhorse. Not wildly powerful, but it does an otherwise fantastic job getting me around and I enjoy it for all of its other qualities. It could use more power uphill (it slows to single digit kmph on some of my daily hills, but I understand 500W nominal power is intentional to be accepted in more jurisdictions.
Update 1: I think I have isolated it to the front brake, or nearby. When I squeeze it moderately, I can rock the scooter which causes a knocking sound. if I squeeze it more firmly, there is no knocking sound. I'm unsure if this is truly the brake, or if it's just preventing me from rocking it as effectively to cause something else to knock. Video demonstrating this:
Original:
Link to video where you can hear the issue:
https://youtube.com/shorts/0z4arejb_4I?feature=share
Brand new scooter. After the first ride, I noticed a sound, like creaking plastic coming from somewhere. I can't quite pinpoint it as I can only replicate it while riding and haven't been able to get my head low enough to sort out the location. Both fenders seem bolted on solid, and jumping to flex the suspension is silent. I only notice it while rolling on old asphalt or surfaces with minor imperfections.
Edit: thanks for the suggestions. I'll report back if I figure it out.