I don't understand how this works, can someone explain. Are lightsabers touch sensative? Is that why when a Jedi dies or loses his or her saber it automatically deactivates?

And i'm sure you can rule out buttons, because at times a Jedi would fight with one hand (like Dooku) and the blade would still be ignited when we know that Dooku or Darth Tyranus' button on his hilt is near the bottom.

But we see Anakin walking down corridors twice with deactivated lightsaber in hand (once going into the Temple and the other going to "take care" of the Seperatist). He's touching his saber but no blue blade is shining? Why is this? How do these darn things work?