Montoring notes, rather than operating notes, as I was just listening to this net.
On the first Saturday of each month, the Washtenaw County sirens are tested at noon, March through October. A net on the N8DUY 145.15 repeater assists in this testing. Radio operators are encouraged to register in advance and to identify a siren to watch. In general you are looking for good sound, good rotation (for sirens that rotate), and any maintenance issues. The net convenes at about 11:30 a.m. and is done by 12:15 p.m. or so.
There are 87 warning sirens in Washtenaw County that are managed by the county. City of Ann Arbor sirens are under city management and are tested on a different schedule.
The N8DUY repeater has very good coverage and is well tested making it ideal for the task of providing coverage to the whole county. This month's net was well-run and verified the correct operation of sirens from Manchester to Northfield Township to Ypsilanti Township.
If you're interested in participating in this testing, contact Ben KC8NIY.