Every time we check our phone we receive a dopamine kick from our body. This basically makes us addicted to our smartphones and computers. In my experience this is even stronger for managers that always have someone to respond to.

If your workshop participants are glued on their smartphone, they won't be much concentrated on the workshop. But sometimes, when you use the rule of "no smartphones" they might not be concentrated either as the fear of missing something is too high. 

The "I need a Dopamine Fix" card is a one time pass that you give to each participant. By using this card they can go check their phone, make that phone call or respond to that very urgent email. Now they can leave their smartphone knowing that if it's really needed they can get that Dopamine Fix. 

Yep, we are all junkies.