You’re welcome! Unfortunately, if you want the slot to affect the conversation (this includes just checking whether it’s set or not), you’ll have to write a rule for every slot value. We are considering allowing “OR” for slots, but this is still in discussion.
If it’s set to influence_conversation: true, then you’d have to do it for every possible value of the slot. If it’s not set to influence_conversation the rule will apply whether or not the slot is set.
If you have very many values for the slot, but you still want the rule to apply only if the slot is set, you could get around writing a rule for each value of the slot by creating another slot. This would be a boolean: true if the slot DEVICE was set, and false if the slot DEVICE was not set. You can have this boolean slot set internally, in a custom action triggered (for example) by the intent used to set the DEVICE slot. Let me know if you have questions about this last part.