A report released Tuesday by the Government Accountability Office shows there are more contraband cell phones in federal prisons than in 2008.

From Hillicon Valley:

The Bureau of Prisons confiscated 3,684 cellphones in 2010 compared with 1,1774 cellphones in 2008. The majority of those cellphones were in minimum security institutions, but more than a thousand confiscated in 2010 were in low, medium and maximum security prisons.

The report suggests prisons take a look at how they’re detecting cell phones. Right now, most prisons use metal detectors. In its report, the GAO said it did not support the use of jamming cell signals to stop the use of contraband cell phones because this technique can mess with signals outside of prison walls.