The literal meaning of this Irish term is "Guardians of the Chicks" (or "chickens") and is used in Ireland to refer to the national police force Garda Síochána na hÉireann or the "Guardians of the Peace of Ireland". The term is somewhat pejorative and is used disparagingly if jokingly.
When we had the bomb scare the Garda Sicíní was everywhere standing around uselessly talking about Sunday's match at Croke Park.
A glimmer man (sometimes rendered as "glimmerman") was a name unofficially, but universally, applied to inspectors who were employed by coal gas manufacturers in Ireland to detect the use of gas in breach of rationing restrictioons during the Emergency (ie. WW2) from March 1942 and in some places as late as 1947.
The term is now used as a metaphor for bureaucratic intrusion into privacy.
"Rattled by the glimmer man, the boogie man, the holy man" - lyric from "Faithful Departed" by Phil Chevron.
"Gas could be used only on certain hours of the day and hence the arrival of the Glimmer man."