I had one of these on my keychain thatI bought in a parts store off the counter for about 2 years but then my keys got ran over and I wanted another to replace it. So I bought one from here and it showed up reading pressures from really low to really high every time I used it. Upon further inspection I realized that it was broken inside and the two black plastic halves were moving. Don't buy these. There is no telling if you will get a working one or not.