The cell phone. Most of our information about our life can be found there: what you said, what you saw, where you went. Be careful what you say and do with your cell phone or ipad, it could end up being the confession you never intended.
Think about what would happen if the police had the ability to go through your phone after pulling you over for suspected DUI. What if that last text you sent an hour earlier to your friend said "man, I am so drunk. I gotta go home." Or, consider being stopped for a suspected battery and you texted your best friend in anger "that jerk deserved to get his teeth knocked out and never saw it comin." Consider what would happen if the police find directions to the site where you bought drugs, or met with someone suspected in a crime? If these searched by police are allowed, you may have incriminated yourself.
The FBI recently investigated a college student who claimed to have made a small amount of ricin, a deadly poison. Because the student told a questioning agent that he had learned how to make the poison through research done on his iPhone, the FBI attempted to gain evidence through search and seizure of the device. The search warrant was denied by the District Court for the District of Columbia, however, on the grounds that it was overbroad. While the warrant application did specify that only the browsing data on the specific phone would be used, it is difficult to understand the limits in scope of this type of search.
This occurrence is just one example of prosecuting parties intending to search a defendant's smart phone for evidence. Other instances explored by Ars Technica have brought up an even more basic question: should police be permitted to search a cell phone without a warrant at all? It is true that police currently are allowed to search all personal items an individual has on them when s/he is arrested. However, given the vast amount of personal information now connected to someone's cell phone (one could easily uncover incriminating photos, text messages, browsing history, social media activity, and so on), that search is in ways just as invasive as a search of someone's home. The Supreme Court is expected to rule in June on two cases in which prosecutors are attempting to use information obtained through unwarranted search and seizure of personal cell phones. These rulings will likely help clarify the future of these types of cases.
The ability for any prosecuting party to search through an individual's smart phone—even with a warrant, if it is not narrowly defined—could have serious privacy implications. Consider a police officer obtaining a warrant to physically search a person's apartment. It would not be reasonable for that officer to then search every other unit in the same building based on the grounds that they are all connected. Likewise, it would not be reasonable for a police officer to have the ability to search through the whole of an individual's smart phone data while looking for ricin research (if the officer stumbled upon a Facebook conversation in which a friend admitted to possessing marijuana, could that friend then be convicted of a crime?). Currently, it is deemed too difficult to differentiate in detail between types of data in a way that would allow lines to be drawn for the purpose of a warrant. Until a firm precedent is set that protects individual privacy in regards to cell phone usage, it seems the best advice might be to treat your phone as you would treat your home: if you don't want anyone wandering in, lock it.