Which of the following is essential to prove unlawful restraint?

To establish proof of unlawful restraint, it is essential to demonstrate that an individual has restrained another person's liberty without lawful privilege. This means that the person doing the restraining lacks the legal authority or justification for the action taken. Unlawful restraint hinges on the absence of privilege, which differentiates it from actions that may be legally justified, such as detaining a person under certain legal circumstances.

Using physical force or threats may be involved in some cases of unlawful restraint, but it is not a requisite for proving the act itself. Similarly, securing a warrant for detainment is a legal mechanism that provides authority for confinement in specific situations, thus falling under the category of lawful privilege. Obtaining consent from a guardian also does not relate directly to the standard of proving unlawful restraint regarding liberty; doing so may lead to lawful restraint depending on the circumstances, but it does not define the essential elements needed to prove an unlawful act.

In conclusion, the core element of proving unlawful restraint is demonstrating the lack of privilege to restrain someone's liberty, which is fundamental for establishing such a legal claim.