Among the listed methods, which is the least effective for delaying an attacker?

The least effective method for delaying an attacker is open access points. Open access points provide little to no resistance against intrusion, allowing an attacker to enter a facility with ease. When there are no physical barriers or security measures in place, the attacker can bypass any security protocols simply by walking through these vulnerable areas.

In contrast, physical barriers such as locked doors or reinforced entryways serve to hinder unauthorized access, while alarm systems can alert security personnel or law enforcement in the event of a breach, effectively delaying the attacker's progress. Security personnel are trained to respond to intrusions and can intervene before an attacker reaches their objective, thus providing a significant delay.

Open access points lack any of these deterrent qualities, making them the weakest method in terms of physical security and delay in the face of potential threats.