GREENSBORO, NC -- Did you know -- every card, letter or parcel you put in the mail will be scanned? It's not so you can track your mail if it gets lost, but rather so authorities can track you if you're suspected in a crime.

2 Wants To Know started looking into this mail surveillance after seeing it used in CBS' hit show Hunted -- where nine teams act as fugitives and try to evade capture for 28 days. In episode 2, one team of fake fugitives tried to outsmart tech-savvy investigators by using old school communication.

"A few days ago we mailed letters to a group of people with instructions on how to communicate with us using a draft system in a secret e-mail account. That makes this whole process virtually untraceable for the hunters," explained a contestant.

Untraceable? Hardly. Hunted's real-life investigators caught wind of what the contestants were doing, when they obtained letters appearing to be written by the same person with the same return address. But, how did the hunters get their hands on those letters?

Turns out, the US Postal Service scans every piece of mail. Law enforcement agencies can request those scans for persons of interest in felony or fugitive cases. The process is an investigative tool called "mail cover."

North Carolina SBI assistant special agent Gerald Thomas told WFMY News 2 if he received mail cover, the USPS would send him information about who the mail is going to, who it is coming from and the postmark -- but he wouldn't get the actual piece of mail.

"We are certainly not reading your mail, and the Constitution under the Fourth Amendment wouldn't allow us to open the mail without some legal process," Thomas explained.

WFMY News 2's Meghann Mollerus talked to the NC postal inspector, who referred her to USPS Communications, who didn't return calls for comment. But, she found a 2014 audit report that showed USPS processed about 49,000 mail cover requests the previous year. The audit found not all requests were processed in a "timely manner," 21% were approved "without proper authorization" and 13% were not justified or accurately transcribed. But, do those issues really matter?

"I cannot think of any case this office has used it for in 10 years," Thomas explained. He said the only case he can recall requesting it for was a financial case, which the mail cover didn't help solve.

So, Thomas said the best investigative tool is even older than mail and smarter than social media.

"A lot of it still depends on good old police work as far as talking to people, witnesses, neighbors, loved ones -- just back to the basics."

So, if Hunted's faux fugitives don't want to set off more red flags with investigators, they had better realize only face-to-face conversation can be fool-proof.

Watch Hunted on Wednesdays at 8/7c on WFMY News 2. Catch up on full episodes for free via CBS.com.