OS X El Capitan: Use Find My Mac
If you misplace your Mac, iCloud Find My Mac helps you locate it. Before your Mac goes missing, make sure you set up Find My Mac and know how to locate your Mac using an iOS device or another computer.
As long as your lost Mac isn’t in sleep and is connected to a Wi-Fi network or tethered to a personal hotspot, you can locate it on a map. If it’s connected to the Internet via Ethernet, Wi-Fi, or a personal hotspot, you can play a sound on it, lock it, or erase it completely.
Set up Find My Mac
Choose Apple menu > System Preferences, then click iCloud.
If you’re asked to sign in, enter your Apple ID or, if you don’t have one, click Create new Apple ID, then follow the instructions. If you already have an Apple ID, you should use the same email and password to set up iCloud on your Mac and your other devices.
Turn on Find My Mac.
If a Details button appears next to Find My Mac, click the button, click Open Security & Privacy, then click Enable Location Services.
The Details button appears if Location Services is turned off in Security & Privacy preferences.
If Enable Location Services is dimmed in Security & Privacy preferences, click the lock icon , then type the name and password of an administrator for the computer.
For added security, make sure all user accounts have secure passwords and that automatic login is turned off in Users & Groups preferences. For instructions, see Change the login password and If you don’t see a login window when you start the Mac. To open Users & Groups preferences, choose Apple menu > System Preferences, then click Users & Groups.
Find your missing Mac
When you need help finding your Mac, do either of the following:
On another computer: Go to icloud.com/#find to use the Find My iPhone web app on iCloud.com.
You can also go to iCloud.com, sign in, then click Find My iPhone.
For more information, see iCloud Help.
On an iOS device: Use the Find My iPhone app.
For more information, open the app on your device, then tap Help.