Autosequencers are a part of Federation transporters.
When Ambassador T'Pel was beamed to a Romulan warbird, her signal started to degrade so additional power was diverted to the autosequencers. It was to late, and T'Pel was apparently lost (in truth she was beamed away by the Romulans) and a transporter diagnosis was conducted. As could be expected, it was discovered that the autosequencers were functioning normally. (TNG: "Data's Day")