The government's argument in this case seems fairly reasonable. Conducting an in-person search of a cellphone after the suspect has been arrested seems similar

The government's argument in this case seems fairly reasonable. Conducting an in-person search of a cellphone after the suspect has been arrested seems similar to going through a bag they're carrying. The WaPo article argues that the storage capacity of modern cellphones should make them legally different (even though the phone in this case was a dumb phone), but I'm not sure how such a legal standard would work. I suppose one approach would be for police to be able to search things physically on the phone (like contact lists) but not things that the phone simply gives them access to (like email, social networks, bank info, etc). The problem with a smartphone is not so much that it contains a ton of info, but that it serves as an access point to a lot of personal info that would otherwise require a warrant to obtain. Maybe the legal analogy would be that police can't search your house without a warrant after they arrest you even if you have your house keys on you at the time. They can search your belongings but can't use those belongings (like keys) to conduct further warrantless searches.