The Regulations Governing Labor by Prisoners Article 25

According to its management needs, the prison may allocate a cell to the prisoner for the external work who, upon returning to the prison, shall undergo physical, clothing and belonging inspection, as well as tests of narcotics (drugs), alcohol, and urine.
中文原文 受刑人作業實施辦法第25條
監外作業受刑人,監獄得依其管理需要配房。
回監時,應檢查其身體、衣類及攜帶物品,並得實施毒(藥)物、酒精檢測及尿液檢驗。

English translation for reference only; the Chinese text prevails. Not legal advice.