I dont think it was about telling there was another timeload, I thought the timeloads arnt telepathically linked, it was all about the watch getting opened, and the energy release, thats how the Family of blood found him.
----------------------
Time for a Sexy Party!
----------------------
but in Human Nature and the Family of Blood, he used the Camelean Arch to Change into a human,
The Timelords essents were stored in a pocket watch with timelord writting on it,
the Same watch was held by the Master, so.. when the watch was opened, the essense escaping back into the human, and turning them back to a timelord was felt by the other one. er.. or something
----------------------
Time for a Sexy Party!
----------------------
The Doctor can sense another Timelord - but the Master wasn't a Timelord, he was a human.
That's why when he opens the watch, the camera switches to the Doctor and he looks shocked and scared, or whatever - as he can then sense another Timelord.
It was just explained in today's episode why he couldn't notice him as a Timelord in the other episodes.
Something to do with the Archangel or something..
I thought parts of it were a bit convenient and contrived, but overall a damn good episode. Barring that song near the end, but the moments after it oooh it's all so good. Shame that the next episode will be the last one till xmas. SOBS.