What is a “probation detainer”? Answer: When a person is on probation and they do not obey the terms of their probation, the probation officer assigned to the case can asked that the person be locked up. The most common time when this happens is when the guy that’s on probation “catches a new case”. When this happens that person is required by law to contact his probation officer who may then ask them to report directly to the probation officer. 
In the meantime, the probation officer prepares what we think of as a “bench warrant”: something that can officially hold the alleged probation violator in jail until they go before a judge for a probation violation hearing. This bench warrant type thing, when used in the probation setting, is called a “detainer” because it serves as notice for all law enforcement that come in contact with that person to “detain” them for being violation of their probation. Montgomery County probation violations almost always start with the “detainer”.
Detainers are lodged by probation officers. When someone gets a detainer and go to jail there is no bail hearing. They stay in jail until the case the probation violation case is heard by a judge in Norristown. In very rare circumstances the detainer can be lifted and the person can leave jail as he waits for his probation violation hearing. Only a judge can “lift” a detainer and allow the person to go free. As a Montgomery County Criminal Lawyer, I have had occasion to petition the court to lift a detainer, and with a degree of success. But this relief is the exception rather than the rule. Most of the time, it is still worth a shot. If you or a loved one has a Montgomery County probation detainer you should contact an attorney skilled in the Pennsylvania Probation system.