I’ve seen a lot of security devices for travelers, but many of them tend to be alarms that sound when someone attempts to open the door. The Veritas Travelers Doorstop is designed more to keep out intruders than to merely alert you to someone breaking in. It’s made of a solid aluminum wedge with a hardened steel adjustment- and anti-slip screw. Simply slide the wedge under the door and use the screw to elevate it until the door is solidly wedged closed. Should anyone push in against the door, the Veritas simply wedges in tighter and the pointed screw digs into the subfloor to keep the door from sliding open.
The wedge works with both concrete and wooden subfloors, and there will be no damage to either the carpet nor the subfloor if no one tries to force open the door. Veritas weighs only 7 ounces, and it comes with its own travel case. It’s available for $29.50 from Lee Valley Tools.