Are you using vanilla ender chests? I checked the horizon mod list and ender storage isn't there. Vanilla ender chests isn't considered an inventory, and only the player can interact with them.
I think you are thinking of a Redstone clock. Easy method is to use a Redstone clock from extra utilities. However I'm not sure if that can be turned off. Of you can use good old vanilla clocks like the comparator clock.(Search for it)