An espagnolette is a locking device

Lock (device)

A lock is a mechanical or electronic fastening device that is released by a physical object or secret information , or combination of more than one of these....

, normally mounted on the vertical frame of a French door or casement window

Casement window

A casement window is a window that is attached to its frame by one or more hinges. Casement windows are hinged at the side. A casement window (or casement) is a window that is attached to its frame by one or more hinges. Casement windows are hinged at the side. A casement window (or casement) is a...

. A handle or knob is connected to a metal rod mounted to the surface of the frame, at about three or four feet above the floor. Operating the handle rotates the rod, which has hooks at each end that fit into sockets at the head and sill of the opening. This type of lock is often used on a semi-trailer truck

Semi-trailer truck

A semi-trailer truck, also known as a semi, tractor-trailer, or articulated truck or articulated lorry, is an articulated vehicle consisting of a towing engine , and a semi-trailer A semi-trailer truck, also known as a semi, tractor-trailer, or (in the United Kingdom and Ireland) articulated truck...

 to fasten the rear doors. It can be identified by the use of a round bar, instead of a half-round bar used on a crémone bolt

Crémone

Crémone or "Crémone Bolt" is a type of decorative hardware used as a locking device to fasten a pair of swinging windows or "French doors". A knob or lever handle is linked by a rack and pinion gear to a pair of half-round rods or "surface bolts" which slide over the outside surface of the door or...

.

In the photograph, the decorative lever arm (1) is hinged to rotate 90 degrees out of a metal "keeper" bracket (2), and then pull away from the surface of the door, which rotates the round metal rod (3), and also the hook at the bottom of the rod to unfasten the mechanism from the metal "stop" (4) mounted on the floor and unfasten the door leaf. The rod, hook and stop at the top door head are not pictured. Note that the door leaf swings outward, and this kind of stop presents a tripping hazard when used at a door sill.