Once again the credit must go to Spiel und Kunst mit Mechanik for finding this great resource.
Shown above is a diagram of Hero of Alexandria's clever method for automatically opening temple doors. The fire in the pot, creates pressure in the large water tank. This causes water to spill into the bucket, the weight of which works against the counterweight to rotate the vertical axle attached to the temple door. Very clever. Done with the right amount of ceremony, this must have seemed very magical indeed to the ancient Greeks.
Here is a link to the photoset associated with the article. If you are able to read German, you might also like to read the original article on automata in antiquity.
[ Thanks once again to Falk Keuten! ]