January 19, 2012 11:01AM # “You could use it at a specific event. You could use it at a shooting-prone location…” By [Jim Harper](https://www.cato.org/people/jim-harper) --- SHARE That’s NYPD Commissioner Ray Kelly touting a new technology called “terahertz imaging detection” to [a local news outlet](http://newyork.cbslocal.com/2012/01/17/nypd-testing-gun-scanning-technology/). Terahertz radiation is electromagnetic waves at the high end of the infrared band, just below the microwave band. The waves can penetrate a wide variety of non-conducting materials, such as clothing, paper, cardboard, wood, masonry, plastic, and ceramics, but they can’t penetrate metal or water. Thus, directing terahertz radiation at a person and capturing the waves that bounce off them can reveal what is under their clothes without the discomfort and danger of going “hands-on” in a search for weapons. Many materials have unique spectral “fingerprints” in the terahertz range, so terahertz imaging can be tuned to reveal only certain materials. (In case you’re wondering, I got this information [off the top of my head](http://en.wikipedia.org/wiki/Terahertz_radiation)…) Will the machines be tuned to display only particular materials? Or will they display images of breasts, buttocks, and crotches? The [TSA’s “strip-search machines](https://www.cato.org/strip-search-machines-a-loss-seeds-the-win/)” got the moniker they have because they did the latter—until the agency tardily [re-configured them](http://thenewamerican.com/usnews/politics/8295-tsa-announces-privacy-changes-in-security-checks). Then there’s the flip-side of not going “hands-on.” Terahertz imaging detection doesn’t natively reveal to the person being searched that law enforcement has picked him or her out for scrutiny. A pat-down certainly lets the individual know he or she is being searched, positioning one to observe and challenge one’s treatment as a suspect. Terahertz imaging lacks this natural—if insufficient—check on abuse. So terahertz imaging is not just a “hi-tech pat-down.” Its potential takes what would be a pat-down and makes it into a secret, but intimate, visual examination—a surreptitious strip-search. Pat-downs and secret strip-searches are very different things, and it is not necessarily reasonable, where a pat-down might be called for, to use terahertz imaging. And that brings us to the fundamental problem with Commissioner Kelly’s proffer to use this technology at a “specific event” or at a “shooting-prone location.” These contexts do not create the individualized suspicion that Fourth Amendment law demands when government agents are going to examine intimate details of a person’s body and concealed possessions. It is certainly possible to devise a terahertz imaging device and a set of use protocols that are constitutional and appropriate for routine, domestic law enforcement, but Commissioner Kelly hasn’t thought of one, and I can’t either. Consider the dollar costs and potential health effects of terahertz imaging detection, it might just be that the pat-downs pass muster far better than the high-tech gadgetry. ##### Related Tags [Technology and Privacy](https://www.cato.org/technology-privacy) [![Creative Commons License](/build/cato_2020/images/creative-commons.svg)](http://creativecommons.org/licenses/by-nc-sa/4.0/) This work is licensed under a [Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License](https://creativecommons.org/licenses/by-nc-sa/4.0/).