The Magic Intercom

My office's entrance is a pair of wooden doors that are unlocked by tapping your card on the scanner next to it.
Because I am a part time staff, I do not have the card, so I was told to press the Intercom button next to it.

Now, I wasn't told what to say when I pressed the Intercom.
And the thing is, anyone in the company can answer the Intercom. Even I know how to pick up the phone and let the person in when the Intercom rings. However, I don't think anyone actually knows exactly WHAT to say when you pick up the Intercom.

So yesterday morning I pressed the button and after like 10 seconds of fumbling noises, me saying 'Hello, I'm Alan' to seemingly noone, the door suddenly unlocked, so I entered.
Today, after I pressed the button for 3 times, someone finally picked up, but said something unintelligible. It did not sound like "Hello", "Good Morning", or "Who is this?". 

The last response is probably the most appropriate response, since you want to know who the hell is at the door before letting them in right? However, I have a feeling most staff here don't really know EVERYONE in the company, so they won't know who to let in either. (They definitely won't know who I am since I"m only a temp)

I wonder what I should say into the intercom next time.

Maybe I'll try 'Open Sesame'.