Many countries have a single emergency telephone number, sometimes known as the universal emergency telephone number or occasionally the emergency services number, that allows a caller to contact local emergency services for help.
Obviously, one would have to have access to a phone. In the case of an unlawful detention, how can we reproduce the same mechanism with something more... "discrete"?
Knowing that in a lot of cases,
those imprisoned are fully searched, their clothes and items confiscated...