I bought my first digital thermo/hydro meter at a pet store for $25. Later that week I found them at Wal-Mart for $7. I now have a few of them at different places in the housing. What's the difference between the $25 meter and the $7 one? The expensive one came with a AAA battery

I am using stick on tiles I bought from the local home center for $.88/each. They look great and clean up is quick and easy.