March Who Madness: Day 26
Day 26: Favorite Doctor Gadget
He pulls this thing out of nowhere (like he always does) and uses what looks like a car mirror to see the invisible critter, then inputs the data in the TARDIS to find out what it is. I. Love. This.
I don't know why, but this gadget stood out in my mind above all the others. Maybe it's because it's also a favorite episode. Maybe.