Activater objects are a "switch" for nearby activated objects such as Open on Activate and Change on Activater. They are triggered by a player touching them. This activation lasts for a few seconds and then is reverted.
Open on Activate
Open on Activate objects react to nearby Activaters and slide open. They are collided with when closed and can be passed through when open.
Change on Activate
Change on Activate objects react to nearby Activaters and change cells.