suspicious object; suspicious substance
Used especially in security contexts for unattended bags, packages, or unknown substances that may pose a threat.
A suspicious object was found at the station, and the police are investigating.
If you find a suspicious object, please notify a staff member immediately.
危険物 means 'dangerous goods' or 'hazardous materials' in general, whereas 不審物 emphasizes the suspicious nature of an object whose danger is not yet confirmed.
Compound of 不審 (ふしん, 'suspicious, doubtful') and 物 (ぶつ, 'thing, object').