You must check out visitors when they leave.
Watch this video to learn more. Click the Captions icon (CC) to turn on video captions in one of the available languages. If using Internet Explorer, the video might not display. To fix this, open the Compatibility View Settings and clear Display intranet sites in Compatibility View.
To check out a visitor:
If the visitor was assigned a credential, the credential status switches to Unassigned, and can be assigned to another visitor or cardholder. The credential is also removed from all access controllers it was synchronized with. This might take a few seconds.