PBS News Hour reported on November 28, 2022, that —
McCarthy has assured that under his leadership, the House will remove the metal detectors that were installed to prevent firearms in the House chamber; ...
Given that McCarthy had assured removal of the metal detectors and moved into the Speaker's office, it seems, at least possible, that security officials removed the metal detectors just before noon on January 3rd, without explicit authority, knowing (or suspecting) they would otherwise be ordered to remove them later that day. In the absence of a Speaker or authority to assess fines, there would be no particular reason to have them remain.
The Sergeant at Arms is an officer of the House of Representatives, elected by the members and one whose term does not expire on January 3rd with a ending of a term of in Congress. The Office of the Sergeant at Arms has responsibility for, among other things, "House Security", which includes the installation and use of the metal detectors throughout the House side of the Capitol, such as entrances for the public.
As reported in the New York Post, January 12, 2021, —
Lawmakers will now be required to walk through metal detectors before entering the House of Representatives chamber in the wake of the Capitol riots.
The acting Sergeant At Arms announced on Tuesday afternoon that magnetometers had been placed at selected entrances to the chamber and reminded lawmakers that firearms were forbidden.
“Effective immediately, all persons, including Members, are required undergo security screening when entering the House Chamber,” the statement read.
“Failure to complete screening or the carrying of prohibited items could result in denial of access to the Chamber,” it went on.
Based on the timeline from various publicly available sources, one can surmise this sequence of events.
After the breach of the Capitol on January 6th, 2021, then-Sergeant at Arms, Paul Irving ordered installation of the metal detectors.
On January 7, 2021, Paul Irving's resignation was announced by Speaker Pelosi and, on January 12, 2021 (date of oath), Deputy Sergeant at Arms Timothy Blodgett became acting Sergeant at Arms. Blodgett oversaw the installation and use of the metal detectors until his replacement on March 26, 2021.
As of March 26, 2021, William Walker became Sergeant at Arms through January 7th, 2023.
William McFarland became Sergeant at Arms on January 7, 2023.
The only person with senior authority to order removal of the metal detectors on January 3, 2023, was William Walker.