Whilst the default is that magic items are only triggered if you're holding them, I don't think you necessarily need to go to great lengths to change away from the default - otherwise magical traps would become much more difficult. Linked / environmental triggers are required when you want something that isn't a standard physical action (e.g. mind reading, astrological changes), but verbal commands are explicitly included in the standard list of activations on page 98 of the core book - it's just usually you set up your Pilum of Fire wand so it only goes off when you say Burn, not when anyone standing nearby you does.