should the FBI be allowed to use cellphone data without a warrant?

No, the FBI shouldn't be allowed to use cellphone data without a warrant. The FBI should have a warrant if they want to use cellphone data. It's basically stocking if the FBI uses your cellphone data without your permission. If they're looking for a guy who committed a crime they could find your data in the area and turn you into a suspect. Another reason is you have no clue when they would be tapping into your cellphone data. So you don't know if your being followed or accused of something. The FBI shouldn't be able to use cellphone data without a warrant.