In the DC Metro system: What are these things (link to photo included)?

You can find a photo of what I'm asking about here:

<a href="http://www.flickr.com/photos/85697... title="Photo Sharing"><img src="http://farm2.static.flickr.com/1300... width="700" height="850" alt="metrodevice" /></a>

or if the above doesn't work, click here:
http://img.photoamp.com/i/K279M.jpg

They are usually located at the entrances of Metro stations within DC, right alongside where the steel gate that close the sations are located. Each device has a connected line that perhaps supplies power.

Ever since I took identify I've been curious what they are. I hope someone out at hand can enlighten me. Thanks!



Answers:   
I'm guessing that they are alarms.
They are the transient deterrent system and are designed to electrocute the bums as they try to enter the subway to spend the hours of darkness. Quite possibly some type of emissions sensor. Carbon monoxide, or something similar. I cant narrate it they are wires or copper tubing coming into the top, so they could be a part of the fire system as resourcefully.


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