TARDIS Home beacon

[Lipzo]

I've been binge watching a lot of Tennant's episode's and I've noticed there have been a few times he wanted the TARDIS but couldn't get to it yet Smith's version could home in on the key for it. I was just wondering if there had ever been an explanation for this.

The only thing that I can think of is that at the beginning of Smith's run, they physically showed the key once the TARDIS had finished rebuilding itself.

[newbaggy]

As far as I remember, the key being used to summon the TARDIS only occurred once. in The Time of The Doctor. In that case, the Doctor had wired "Handles" into the console so that it could control the TARDIS in his absence. The Doctor could not recall the TARDIS in other episodes because there was no-one aboard to fly it. Patrick Troughton'e Doctor occasionally used a "Stattenheim remote control" to retrieve his TARDIS, but subsequent Doctors appear to have lost it. Otherwise, the TARDIS will only fly unmanned in response to the activation of one of its emergency protocols (e.g. Emergency Program One, the Hostile Attack Displacement System, etc.), or if a pre-programmed control disc (Blink) or control device (Time of the Doctor) is inserted into the appropriate interfaces on the console.

[Lipzo]

As far as I remember, the key being used to summon the TARDIS only occurred once. in The Time of The Doctor. In that case, the Doctor had wired "Handles" into the console so that it could control the TARDIS in his absence. The Doctor could not recall the TARDIS in other episodes because there was no-one aboard to fly it. Patrick Troughton'e Doctor occasionally used a "Stattenheim remote control" to retrieve his TARDIS, but subsequent Doctors appear to have lost it. Otherwise, the TARDIS will only fly unmanned in response to the activation of one of its emergency protocols (e.g. Emergency Program One, the Hostile Attack Displacement System, etc.), or if a pre-programmed control disc (Blink) or control device (Time of the Doctor) is inserted into the appropriate interfaces on the console.

Ah alright.
Though the question still reamins, why hadn't he done that in the first place (beside's the obvious fact of convenience writing).

[DarthSkeptical]

Eleven is not able to just touch the key and make the TARDIS appear. That's a mis-interpretation of what's going on in "The Eleventh Hour". In fact, they key is glowing because the TARDIS is alerting him to the fact that she's "done cooking". In other words, it's much more like a proximity alarm than anything else.

This has a substantial precedence in the BBC Wales series, stretching all the way back to S1E4, when Rose's newly-obtained TARDIS key glows to signal that Nine is on his way back to her council estate. Later, in S1E8, it rather memorably tells the Doctor and Rose — through its heat and gloowiness — that it's coming back through the wound that's been caused in time by the paradox of Rose touching herself as a baby. Yes, the TARDIS materialises around the key — so in that sense it's bringing the TARDIS to the Doctor — but these are extraordinary circumstances. The Doctor isn't causing it to bring the TARDIS forth; the key is alerting the Doctor to the TARDIS' arrival. Later still, in Blink, we see the TARDIS is capable of detecting the DVD and making it glow, precisely as it does with keys. So the TARDIS is, without any sort of pilot on board, completely able to detect "important" objects, and make them glow, upon simple proximity.

And there are other cases, but there's no need to laboriously list them.

Newbaggy is correct to point out that The Time of the Doctor is the lone instance of the key appearing to summon the TARDIS. In fact, the episode has the Papal Mainframe depriving him of his obvious key and then saying, "You could summon your TARDIS [with it]." But he quickly shoots back, "The TARDIS doesn't work by remote control."

So who's right? Likely they both are. The TARDIS key doesn't have the power to be used as an active summoning device. It's really never been shown to have that ability. Even in Time he is not shown to touch it before it starts glowing. The easiest interpretation of the scene is simply that the TARDIS key can be tracked by the TARDIS. It was glowing, not because of anything the Doctor did, but just because the TARDIS was on its way — which is really all that it's ever meant since 2005.

Of course, it's a bit like the Cloister Bell: used when convenient. When does the key light up? Whenever it'll make for a nice bit of sparkle, just as the Cloister Bell is used to sound a note of concern — but not every time there's a problem.

Why does Moffat use it in Time? Cause he wants to explain away Smith's obvious hair piece. Smith, having recently shaved his head in real life for another project, was still bald while filming this final episode. So Moffat uses the old "key under the quiff" gag to allow Smith to remove the piece and thereby show the audience that the reason it looks like a bad wig is because it actually is a bad wig. Clever, really – but such is Moffat's way.