‘I smell marijuana’ is a line used by law enforcement to instigate searches regardless of if any is actually present, but whether this gives them a right to search you depends on the situation.
Here are three scenarios in which a law enforcement officer may attempt to initiate a search based on claims that they smell marijuana, and what your rights are in each of them.
In Your Car
The scent of marijuana has been upheld by courts as probable cause. While operating a motor vehicle in public any grounds for probable cause is grounds for a search. So whether or not you are travelling with cannabis, police can use this claim as qualified reason to initiate a legal search of you and your vehicle.
While Walking Around
Once again, the probable cause ruling comes into effect and police you encounter on the street may choose to stop, detain and search you based on the claim that they smelled marijuana.
In Your Home
You have far more protections in your home than outside of it, and for this reason police must first obtain a warrant to search your home even though they have probable cause.
As always, unless you legally have to, never consent to a search.
If police cannot cite valid probable cause for a crime ask them if you are free to go or are being detained. Without a valid reason to detain you, they must let you go and you should be on your way as quickly as possible.
And NEVER answer any questions, as they will most certainly be used to entrap and/or criminalize you.