Which of the following is a requirement for a consent search to be valid?

A consent search is valid primarily when the agreement to search is given voluntarily by the individual, without coercion or pressure from law enforcement. This principle is rooted in the Fourth Amendment, which protects against unreasonable searches and seizures. For consent to be considered voluntary, the person must have the capacity to understand the situation and make an informed decision.

While other options may raise questions about the circumstances surrounding a consent search, they are not essential requirements for the validity of the consent itself. For example, having a witness is not necessary for consent to be valid, nor is written consent mandatory; oral agreements can suffice as long as they are given voluntarily. Immediate necessity could be an influencing factor in certain scenarios, but it does not directly pertain to the validity of consent itself. Therefore, the cornerstone of a valid consent search is indeed voluntary agreement.