Are continuous monitors a requirement of S20.20?
No, but per ESD Handbook TR 20.20 paragraph 18.104.22.168.4 Test Frequency “Because wrist straps have a finite life, it is important to develop a test frequency that will guarantee integrity of the system. Typical test programs recommend that wrist straps that are used daily should be tested daily. However, if the products that are being produced are of such value that knowledge of a continuous, reliable ground is needed, and then continuous monitoring should be considered or even required.”
Per ESD-S1.1 paragraph 6.1.3 Frequency of Functional Testing “Daily [Wrist Strap] testing may be omitted if constant monitoring is used.”