The round BMW Mini CAS (Car Access System) remotes can come in 2 variants. There is the type that has to go into the slot to start. Then there are the smart/proximity ones that you can keep the remote in your pocket and just press start.
The smart type are used in Mini fitted with ‘comfort access’, although you can program the more basic ones in to vehicles that have comfort access.
If you’ve only got one remote it’s worth considering getting a spare. It’s far cheaper to add a remote to an existing one than it is to replace all missing remotes.