How to prevent iCloud Keychain from being set up on other devices
1. Launch System Preferences either from your dock or by clicking the (Apple logo) on the top left of your screen and clicking System Preferences.
2. Click iCloud.
3. Click Options next to Keychain on the right.
4. Click the checkbox next to Allow approving with security code. This will prevent any of your other devices from accessing your iCloud Keychain.