A random checkpoint is a military and police tactic. In a military context, checkpoints involve the setup of a hasty roadblock by mobile truck- or armored vehicle-mounted infantry to disrupt unauthorized or unwanted movement or military activity and to check for valid identification and search for contraband, fugitives, or weapons that are not permitted in civilian hands. Random checkpoints are set up to achieve surprise, as opposed to known permanently located checkpoints, which suspects could circumvent. They are often established in locations where they cannot be observed by approaching traffic until it is too late to withdraw and escape without being observed. Patrol car-equipped police units regularly use random checkpoints to detect drivers who are suspected of impaired driving. Police also use hastily set up roadblocks to check cars and car trunks when they are pursuing an armed and dangerous fugitive. As with military checkpoints, sobriety checkpoints and fugitive roadblock searches are located in an area where drivers cannot see the checkpoint until it is too late to withdraw, and checkpoints are only set up on a temporary basis. Military use The unit establishing a military checkpoint must carry or obtain the materials necessary to construct it. It might use a large vehicle, or multiple vehicles, such as armored personnel carriers to block the road. In addition to blocking the road with vehicles, the road may also be partially blocked with concertina wire or heavy objects, such as sandbags or concrete blocks. The vehicles might be positioned to partially or entirely block the road or route. The search area might be the space between multiple vehicles. Sentries might be positioned at each end of the checkpoint and are covered by mounted or dismounted machine gun positions. A reaction force may be designated and concealed nearby. Vehicular and pedestrian traffic that approach with the intent of passing flying checkpoints can be asked to produce identification and submit to a search of their persons or vehicle. The trunks of cars are typically searched. In some countries, soldiers inspect the bottom of the car with a mirror to look for bombs. In some cases, people without proper identification or who arouse suspicion may be refused passage, detained, or arrested. Contraband may be confiscated. A random checkpoint must be functional within 15 minutes of the unit's arrival on-site, and establish security teams 50–100 meters on both sides of the area to be controlled. Advanced