In a pending case before a federal district court in Missouri, the government is arguing that use of GPS without a warrant was not unreasonable because officers had reasonable suspicion. In Jones, the Supreme Court decided when GPS use is a search but did not consider when it is reasonable. Here's the language from the magistrate's order (available here):
From this information, the undersigned concludes that the investigating agents had a reasonable suspicion that defendant Robinson had previously engaged in and was currently engaging in criminal activity. The agents believed that tracking the movements of defendant’s vehicle would enable them to confirm or dispel their suspicion. By tracking defendant’s vehicle, the agents would be able to observe defendant’s daily pattern accurately and cost-effectively.
Therefore, the agents did not need to obtain a judicial warrant prior to installing the GPS tracker device on defendant’s vehicle and using the device to monitor the vehicle’s movements. The evidence obtained from the GPS tracker device should not be suppressed for lack of reasonable suspicion.The ACLU has filed an amicus brief before the district court arguing "that warrantless searches are presumptively unreasonable" and the GPS evidence should be suppressed.