This key sold for $23.50 (Plus $2.75 Shipping).
This auction is for an antique steel and brass pocket door key that is signed "YALE". I have never had a signed pocket door key. It measures about 1&5/8 folded and 2&1/8 open inches long. The old Victorian houses had sliding doors which slid back into the walls and these keys were designed for these doors. The key would either slide into itself or fold over so that the key could be left in the lock when the door was opened . The key plate was made with a recessed area around the keyhole to accommodate the bow. - eBay (22 Jan 09)