(S1): Keep locked up

S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. The list was consolidated and republished in Directive 2001/59/EC, where translations into other EU languages may be found. The list was subsequently updated and republished in Directive 2006/102/EC, where translations to additional European languages were added.

These safety phrases are used internationally and not just in Europe, and there is an ongoing effort towards complete international harmonization. (Note: missing S-number combinations indicate phrases that were deleted or replaced by another phrase.)

...
Wikipedia