Did the Doctor's scramble device in The Lodger work on ears?

Question

In Doctor Who's Revived Series 5 episode "The Lodger", the Doctor uses a communication device on scramble to talk to Amy from his gaff on Earth. It seems clear that the transmission channel is scrambled somehow, but what about this segment of their chat:

INT. CRAIG’S BEDROOM, NIGHT

CRAIG gets out of bed and walks to the wall shared with the DOCTOR’S room to listen.

DOCTOR: (through wall) ..Orange juice, eocenes Arbuckle, rare tarantula on the table, ooh!

INT. DOCTOR’S BEDROOM, NIGHT

DOCTOR: I can't go up there until I know what it is and how to deal with it! It is vital that this "man" upstairs doesn't realise who and what I am. (bounces on the bed and smiles) So no sonicking. No advanced technology. I can only use this (taps earpiece) ‘cos we're on scramble. (jumps to floor) To anyone else hearing this conversation, we're talking absolute gibberish.

INT. CRAIG’S BEDROOM, NIGHT

DOCTOR: (through wall) Practical eruption in chicken. Descartes Lombardy spiral.

It seems like the scrambler also affects how other people directly hear the words coming from his mouth. But it's also possible that the Doctor was just being dramatic, knowing that Craig would be listening at that moment (which is the sort of thing we accept that he just knows sometimes, most likely through intuition).

Was it ever confirmed that this scramble device really makes someone sound like they're talking gibberish, even if they're just standing next to you rather than being on the other end of the communications channel?

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Answer 1

If we follow the scene, here's what happens :

Craig hears gibbersish

Cut inside the room.

Amy hears the Doctor.

Cut outside the room.

Craig hears gibberish.

So, if the timeline is respected, we can assume that everything the doctor says is gibberished to people other than Amy.

Since in the end of the episode, there was no twist showing us that for some reason the Doctor actually spoke gibberish when Craig listened, we can fairly assume that the device is working.

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Since it's just a device useful for that particular moment and plot (like so many others), they never bothered to explain how it works. Whether it's the Doctor speaking gibberish and the other side of the line hearing plain english or the Doctor speaking english in the communicator and the device changing it to gibberish to people who can hear.
It isn't explained in the episode, nor in the rest of the season.

Answer 2

Anyone near the Doctor while he was talking to Amy would hear gibberish. This serves two purposes. It protects his flatmates from learning the truth about the Doctor, which would alert the ship upstairs. It also hides the Doctor from the ship upstairs, as it's unable to eavesdrop on the Doctor's communications with Amy.

The scene you've quoted is the confirmation that it works, as it showed the communications from the perspectives of first the Doctor, and secondly Craig. It was a quick way for the writers to show the mechanism working.