Just about all of the jails I've seen in Westerns and in more modern-era TV shows (Andy Griffith Show) have a rear window facing a deserted alley or unwatched area. Whenever the prisoners' friends wanted to talk to, or slip a gun to the incarcerated man, they would do so without any problems. A few times guns would be fired through the window to even a score or kill a protected witness.
Did real jails use mesh or wire instead of iron bars on the exterior walls to prevent this from happening? Or would a deputy be stationed somewhere outside whenever someone was in the jail?