When dialing the other party's phone, if the other party is on the phone, you will hear the prompt "The phone you dialed is busy". This is not that the other party is being monitored, but that the other party is talking to someone else.
If the other party sets the number as a member of the blocked or blocked list, then when calling the other party, the other party will receive an interception notice or hang up the phone directly, which is not that the other party is being monitored.