One of these cheap ones came up months ago. It just gave fake readings all the time, as verified by a reddit sub.
Careful, you get what you pay for.
I bought a similar watch last month from AliExpress. Advertised as measuring blood pressure. Blood pressure was a random number generator between 117 and 125 and between 78 and 84. The last straw was laying the watch on my bathroom sink and getting 122/80. The seller would take no responsibility for selling a fraud, saying "blood pressure cannot be compared with medical equipment, please understand that just a reference range".
These are toys. Only a fool trusts their health to a $35 watch that does something the FDA won't even allow Samsung to do on their high end watches. I bought this one because I liked the look and thought it would be an OK smartwatch, but it isn't even that.