Inside La Tuna, a low-security prison that sits in Anthony, Texas, hundreds of inmates wait for family members to visit them. However, Georgia Martinez, who drove in from Albuquerque, had to stay outside.

"This is the first time they haven't let me in or anybody that's come to see my son," said Martinez. Martinez blames a drug scanner that prison officials use to test visitors for drug residue. They told her she tested positive. Although this is the first time in three years La Tuna has not let her in, Martinez said it's retaliation for speaking out about her son's treatment inside.

"Because I wrote a letter concerned about the conditions there," said Martinez.

KFOX spoke with prison officials, who deny any retaliation. They defended the drug-detection system they use to make sure no drugs or contraband get into the prison.

"The machine is 99 percent accurate. The machine was recommended by the Office of the Inspector General," said Israel Martinez, executive assistant at La Tuna Federal Prison.

For security reasons, La Tuna would not show reporters the actual machine it uses inside; however, we know it looks something like other commercial ion scanners currently on the market. Prison officials said it's almost impossible to manipulate the results.