I've worked on some smaller jets that use a sort of vent plug/panel on the exterior of the MED to lock it out if the airplane's pressurized. I recall being at FSI in Dallas for MX initial for the G200 and the instructors were closely huddled during a coffee break quietly discussing "something", there'd been a mishap on either a 200 or 150 (I don't recall) at Gulfstreams Dallas facility, apparently a line service person opened the door on a pressurized airplane somehow and the door swung out and killed him. I still don't trust those sorts of little devices.