Sapphire crystal is 9/10 on the Mohs scale of hardness. Just for reference, diamonds are 10. It’s nearly twice as hard as standard glass. In practical terms, that means it’s almost impossible to scratch, unless you happen to carry a bunch of diamonds in your pocket. Most watches have mineral glass (5/10 on the Mohs scale) that’s easy to scratch.
Element24 watches all feature sapphire crystal lenses which means that they will maintain their original clarity indefinitely.