Let’s bypass another REX sensor on a door we don’t have access to! The Bypassing Doors blog series demonstrates easy-to-use tools and techniques that can be utilized to bypass an organization’s interior and exterior doors. In this part 4 blog post, we will be discussing how to utilize compressed air! What?!?! You read right! That is exactly what I thought at first – but a can of compressed air will bypass your building’s door.
Many buildings these days are equipped with a “Request to Exit” sensor, or REX sensor. These sensors are implemented due to various regulations and building code requirements.
Request To Exit Sensor
The images below show the Request to Exit sensor (REX sensor) and the way it looks on a door. Typically, these sensors make use of Passive Infrared (PIR) for detection of motion. PIR detects changes in temperature within the area of its field of view.
Photo of a Request to Exit sensor (REX sensor):
Photo of a Request to Exit sensor installed above a door:
Can Of Compressed Air
A really common, inexpensive, great piece of equipment to keep on hand is a can of compressed air (or keyboard dust blaster, as many of us use it for). If you have ever used a compressed can of air upside down, one would know it shoots out cold clouds of air. The compressed air can (pictured below) usually has a small straw that can be protruded under a door frame very easily.
Photo of a can of compressed air, our bypassing tool:
Here is a video of bypassing a REX sensor door with a can of compressed air:
How To Prevent Compressed Air Door Bypasses
There are multiple prevention options that can be implemented to prevent bypassing with compressed air. These options include the following:
Moving The REX Sensor
By moving the REX sensor further away from the door, it can prevent the trigger from sensing indirect motion.
Install kick plates to prevent items like compressed air nozzeles, from sliding items under your doors by minimizing any gap beneath the door.
Implement rubber moldings to prevent unauthorized tools from sliding under the door.
Like rubber moldings, the door shoe adjusts to prevent anything from being shoved under your door.
More Bypassing Doors
If you missed part 1, check out the UTDT post. Here’s part 2, the DDT post. Check out part 3 on REX sensor bypass with a piece of paper. More physical pentesting tools and bypassing overviews are being published soon, so stay tuned for part 5!
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