A detainer is a legal tool employed by a government authority to maintain custody of an individual who is already incarcerated, facilitating a hold beyond the release date for various reasons, including pending charges or immigration status review. This mechanism is typically utilised by law enforcement and immigration agencies to assert jurisdiction over a detainee for additional time, ensuring that the individual does not evade pending legal actions or deportation proceedings. The use of detainers is governed by specific legal frameworks that dictate the conditions and durations under which they can be issued, often leading to complex interactions between different jurisdictions and legal principles, such as federalism and habeas corpus. Critics argue that detainers may infringe on civil liberties and due process, especially when used indiscriminately or without timely judicial oversight. The application of detainers varies widely, influenced by local policies, national laws, and international treaties, reflecting the balancing act between enforcing legal statutes and protecting individual rights.