Basically I will have 3 Pi's running the same script to take synchronised photos. They will be physically very near each other, and I am looking into my options to trigger them at the same time.
My thoughts are:
run a simple flask server - this relies on network connectivity or to have one of the Pis acting as an AP and acting the initiator as well.
a single button or switch which can connect to GPIO input on all 3 devices - I'm not sure how if this kind of thing can be bought out of the box
Are there any other better options to do this kind of thing you guys could recommend?