By detention, in the pre-investigation procedure, one person is deprived of his liberty, which results in limited freedom of movement of that person, with the simultaneous establishment of other restrictions on the detained person. An arrested person, as well as a suspect, can be detained. These persons are detained on the basis of a decision on detention, which is announced, made and served by the public prosecutor, or upon his approval by the police. According to this decision, the detention of a person can last for a maximum of 48 hours. Bearing in mind that this formal act restricts the detained person's proclaimed right to freedom for the purpose of unhindered conduct of criminal proceedings, while freedom of movement is one of the basic human rights in a democratic society, this clearly shows the importance of the legal treatment of the authorities in the pre-investigation procedure towards the detained person, as and the legality of the detention decision itself. In order for the detention of a person to be justified, it must be legal in both material and procedural terms. Otherwise, there would be a legal basis for the detained person to claim damages, due to the arbitrary detention made against him by the authorities. This article points out the formal-legal determinations of the decision on detention, and the rights of adult persons who have been detained for a hearing, with the aim of pointing out some perceived shortcomings after conducting research and analyzing data from the decision on detention and proposing some legal improvements. Keywords: detention, police, public prosecutor, arrested person, suspect.