The Swiss authorities online
The most important Swiss border crossing points are manned 24/7. Many small border crossing points are manned at specific times, and some are not manned at all.
If no border guards are present, you may declare private goods in writing, using the declaration boxes (however, only for goods that are not subject to quantitative restrictions or bans and that do not require a certificate or authorisation). The invoice for the import duties will be sent to you by post later on.