So I ordered another one, and that one died after only one hour of use. It won't even turn on, but it will run when it's plugged in, so it's obviously a battery problem. I contacted Carscam and they insisted that I send it to them for "repair", but, because it doesn't have screws, for them to "repair" it they would need to break open the seal, so it would never be waterproof again. I don't think that's acceptable for a brand new product, especially when I know from my own experience that breaking the seal will probably reduce its life expectancy, which I already know to be quite short to begin with.
Fortunately I have been able to return it through the company I bought it from (Taiwan's equivalent of Amazon) and Taiwan's excellent consumer protection law guarantees me a full refund. But this is a warning to anyone else: stay away from Carscam. Their Google Maps listing is full of one-star reviews complaining of poor follow-up service, and most of their Youtube videos have comments disabled — probably for a reason.
Finally, since most of their products come from China, and Carscam don't offer any worthwhile consumer protection, customers could get the same thing for much less money by just ordering them directly from China on platforms like Alibaba etc.