Minecraft wiki entry for Dispenser, associated text: In addition to the methods above, a dispenser can also be activated by quasi-connectivity.‌[Java Edition only] A dispenser becomes activated if one of the methods above would activate a mechanism component in the block above the dispenser, even if there is no mechanism component there (even if the block above the dispenser is air or a transparent block), but only when the dispenser receives a block update (including a redstone update within two blocks of the dispenser). A dispenser does not activate if it has been less than 1 redstone tick (2 game ticks, or 0.1 seconds barring lag) since its last activation ended.