The moment you notice is always the same. Pockets, then the bag, then the same pockets again.
Before you retrace your steps, do the thing that actually finds phones: open Find My on something else. Minutes matter, because the battery is finite and a last known position ages badly.
Here is the order that works — what to do when the phone is already offline.
What Find My needed to have switched on
Find My depends on settings enabled before the phone went missing. Under your name at the top of Settings, in Find My > Find My iPhone, there are three: the main toggle, Find My network, and Send Last Location.
The main toggle is the map. Find My network lets the phone be located through nearby Apple devices even with no Wi-Fi or cellular connection. Send Last Location makes the phone report its position automatically when the battery is critically low.
If you are reading this in advance, confirm all three now.
Open Find My on another device, or in a browser
Three routes. The Find My app on an iPad, Mac, or other iPhone signed in to your Apple Account. A browser at iCloud.com, where Find Devices shows the same map. Or a family member's iPhone, since a Family Sharing group puts your devices in their Find My app.
That last route matters when the missing iPhone was your only Apple device. Find My on someone else's iPhone has a Help a Friend option in the Me tab, which opens a temporary sign-in without signing them out.
Select your iPhone. Online, you get a live location. Offline, you get its last reported position with a timestamp — read the timestamp, because a location from three hours ago is a starting point, not an answer.
Play Sound before you go anywhere
Play Sound sends an escalating tone that plays even if the phone is on silent. Do it before you leave the building. Phones that slip between sofa cushions, into a coat in another room, or under a car seat get found by sound rather than by map, because a map is accurate to a place and not to a cushion.
If the phone is offline the sound is queued, plays when it next connects, and you get an email then.
Reading the map honestly
Directions opens Maps and routes you to the device's position. Useful outdoors, misleading indoors — a pin cannot tell you which floor of a building or which of four flats.
Turn on Notify When Found before you close anything. It alerts you the moment the phone reappears on the network, which is one of the most useful actions available for a phone that is currently dark. It costs nothing and works while you sleep.
Mark As Lost early, not as a last resort
Mark As Lost does four things at once: locks the phone with your passcode, puts a message and a contact number on the lock screen, suspends Apple Pay cards, and keeps Find My tracking active. You can switch it off in a second if the phone turns up in your other coat, so there is no reason to wait. The message on screen is also how an honest finder knows who to call.
When the phone is offline or dead
An offline phone is not necessarily unfindable. The Find My network relays an encrypted location through other Apple devices that pass near it over Bluetooth, so a phone with no signal on a busy street can still report roughly where it is. On iPhone 11 and later that continues for a period after the phone is powered off, and Send Last Location gives you the position it reported just before the battery gave out.
What defeats it: Airplane Mode switched on from the lock screen, which turns Bluetooth off too, and a phone genuinely out of power. Which is one reason to disable Control Center on the lock screen, in Settings > Face ID & Passcode, before you ever need this.
If it was taken rather than mislaid
Different situation, different steps. Leave Mark As Lost on, and do not go to the map location by yourself — give the address and timestamp to the police, along with the serial number from your device list at appleid.apple.com.
Call your carrier to suspend the line, and change your Apple Account password from another device, particularly if anyone could have watched you type your passcode.
Expect messages afterwards claiming the phone has been found and asking you to sign in. The ones with a link are usually after your Apple Account password, because that is what removes Activation Lock and makes a phone sellable. Never enter those details on a page you reached from a message.
Erase This Device is the last step, not the first, because an erased phone cannot play a sound. On recent iOS versions the device still appears on the map after erasing, and Activation Lock keeps it tied to your account.
Quick answers
Can I find it if Find My was switched off?
Not through Apple. Without it there is no location to look up and no remote lock. You are left with the practical options: call the number, retrace your route, ask venues, and speak to your carrier. Which is why the setting is worth confirming today.
Does Find My work when the phone is powered off?
On iPhone 11 and later it can, for a period after shutdown, because a low-power mode keeps a Bluetooth beacon alive for nearby Apple devices to relay. It is not indefinite, and it depends on Find My network having been on beforehand.
Should I erase it straight away?
Usually not. Erasing ends Play Sound and removes the on-screen message a finder would use to contact you. Mark As Lost first. Erase once you have accepted the phone is gone, or it holds something you cannot risk — Activation Lock stays attached either way.
Will a warning wallpaper help me get it back?
At the margin. A lock screen that clearly belongs to a person, ideally with a way to reach you, gives an honest finder somewhere to go. It does nothing against theft and nothing to prevent unlocking. Find My and Lost Mode are what recover a phone.
Where to get it
For the lock screen itself, DON'T Touch Phone Wallpapers has HD anti-theft and warning designs in a range of styles, from blunt text to minimal, and it is a quick way to put an obvious ownership message on screen before you ever need Lost Mode.
Do that today, along with the three Find My toggles. Together they take less time than the first ten minutes of looking for a phone that is not in your pocket.