Cards with scratches, exposure to debris, and other types of physical damage can be rendered unusable. Key cards may become inoperable when the magnetic stripe is demagnetized through exposure to magnets. Name tags, signs, and purse and wallet closures, and mobile phones are all potential sources of magnet exposure.

The most common reason a hotel key card stops working is demagnetization. Most traditional key cards use a magnetic stripe that stores your room's digital "handshake." If this stripe comes into close contact with a strong magnet—commonly found in smartphone cases, iPad covers, or even high-end magnetic purse clasps—the data can be scrambled or erased entirely. Beyond magnets, physical wear and tear is a major factor; scratches on the stripe can prevent the lock's sensor from reading the code correctly. Friction and heat can also degrade the card's sensitive coating. Another frequent culprit is the "check-out" timer. Hotel servers are programmed to deactivate your card automatically at a specific time on your departure day (usually 11:00 AM or 12:00 PM). If you try to enter your room even five minutes after that window, the lock will deny access. Finally, placing two key cards "back-to-back" in a wallet can sometimes cause electromagnetic interference, leading to a failure at the door.