Lost Mode is a feature in the Find My app that can be used to locate an AirTag or other item registered to your Apple ID if it is lost. When you enable Lost Mode for an AirTag, you can add a message saying that the item is lost and include your phone number or email address. If someone else finds your item, they can use a supported device to see a website with the Lost Mode message. Apple identifies the AirTag as missing, and its system begins searching for it. When someone with a compatible iPhone gets close to your missing AirTag, their phone detects its existence and notifies Apple. Then one of two things can happen: if you enabled notifications when you activated Lost Mode, your iPhone will notify you that your AirTag has been located and will display its position on a map. Alternatively, if someone with an iPhone or an Android phone with an NFC reader comes across your tag, they will receive a notice. They will see the message on their phone if you entered a phone number or message when you set up Lost Mode.