In the US, you have to have six instrument approaches including holding, intercepting etc... within 6 (or was it 12
) months to keep it current. Those can be done in an aircraft or a flight training device.
If you have less in the 12 months I think you're up for a checkride with an instructor, who will then have to sign you off again.
There is a BFR (biannual flight review) too, where you go for a checkride simply to show you can still fly
