When a person thinks about their constitutional protections from government intrusion the Fourth Amendment typically is the first they think about. The Fourth Amendment prohibits unreasonable government searches and seizure of persons and property. These protections are triggered most often when a person is travelling in a vehicle which is stopped by police. The initial stop may have been for some claimed violation of traffic laws. Nowadays as many police departments maintain dash cams it is very easy to objectively determine whether the stop was warranted. A police officer cannot stop a motorist unless he has reasonable suspicion to believe the occupant has violated a law. If the officer did not have reasonable suspicion to stop the vehicle the person can successfully claim his Fourth Amendment right against unreasonable stop and seizure occured. If the court agrees any evidence seized against that person from that point forward may be suppressed by the exclusionary rule ("fruit of the poisonous tree"). So, in that case, filing a motion to suppress evidence would be the proper method to attack the allegedly unconstitutional stop. Next, if the officer searches the vehicle without consent or probable cause (or a warrant) the motorist can attack the search as violative of their Fourth Amendment rights. Other means to bar evidence from trial via a motion to suppress arise when the police officer unlawfully detains a motorist after the point in time where he should have released him with a citation. Many times officers will intentionally delay release of the motorist until a K9 can perform a sniff search of the car. Again, this unlawful delay can cause the judge to issue a suppression order for any items discovered in the vehicle.
The best advice a criminal target can comply with is:
Don't talk to the police more than is absolutely necessary.
Request an attorney if you believe you may be in serious criminal trouble.
Don't consent to a search of the vehicle.
Don't act out of the ordinary.
Following those simple steps can aid you in the future should you be charged with a criminal offense.