Under the Fourth Amendment, the police can’t search you or seize your property without probable cause. Probable cause is commonly defined as a reasonable belief that a person has committed a crime.
Probable cause typically falls into four categories: observation, expertise, information and circumstantial evidence. Police can look at the totality of the circumstances in determining whether they have probable cause. For example, it is perfectly legal to possess plastic baggies, a digital scale, large sums of cash and multiple cell phones. However, if you are pulled over for a valid traffic stop, such as a suspected DUI, and police see all of these items in your vehicle, they could determine that they have probable cause for a search, because these items are indicative of drug trafficking.
You can unwittingly provide the police with probable cause against you. Acting nervous, giving evasive answers or conflicting statements can trigger probable cause when combined with other evidence. The best thing to do is to politely but assertively tell the police officer that you do not consent to a search and that you would like to speak with an attorney. In addition, tell him that you assert your right to remain silent and will not answer any questions without your attorney present.
Under the Fourth Amendment, these are magic words that cut off the police officers right to question you. Make no mistake, if you are in a situation where a police officer is asking you questions, you are a suspect and you are under investigation. Do not make the incredibly common mistake of incriminating yourself!

