This is a nice demonstration of using a scanning pyroelectric sensor to detect people.
The robot chassis appears to be made out of an old answering machine . . .
[youtube=425,350]rmnU_FUi3K4[/youtube]
It appears to have two steps:
If it doesnt see a human (heat source)
keep scanning at large angles
If it does see a human
drive towards the angle that human was detected at
scan at smaller angles as long as human is detected
[youtube=425,350]s_lTQGZtRKY[/youtube]