There is no screening to authorize the use of the contact closure feature in SLS mode. Security is provided by limiting the number of users who know the correct key sequence required for the contact closure feature.

You cannot use the Hold or Transfer features while dialing the contact closure FAC key sequence.

Contact closure will not work until you dial the full digit sequence and it is processed.

If two users try to simultaneously use contact closure, whoever dials the full FAC key sequence first gets precedence.

Interdigit timing rules apply to the contact closure feature, so if you pause too long during the FAC key sequence, the feature times out.

Call appearances are not released (available for calls) until you hang up.

You cannot use the contact closure feature from outside trunk lines.