A knife-wielding ex-soldier held his son prisoner in the family home in what was described as a "siege-like situation".
When gardai arrived, Stepheen Glennon (54) came to the door first with a replica firearm, then with a kitchen knife, before he was pepper-sprayed.
Dublin District Court heard he was estranged from his family and there had been a domes-tic row before the incident happened.
Glennon pleaded guilty to falsely imprisoning his adult son, Richard, at Captain's Road, Crumlin, last March 15.
He also admitted possession of a large kitchen knife.
Judge Anthony Halpin gave him a three-month sentence suspended for 18 months.
Gda Sgt James King said he was called to a "barricade situation" in the house and the accused put a blanket over the window and would not let them in, calling them "scum".
Glennon came to the door with a replica firearm, then went back in. He came out again with a knife and was pepper-sprayed, subdued and arrested. No one was injured.
Judge Halpin said it had been a "pseudo-siege situation".
The defendant was married but separated and had three adult children, his solicitor Stephen O'Mahony said, adding that it was a "very complicated family dynamic".
He said the accused had been in a state of stress, panic and mental ill-health at the time.
"Matters escalated to the extent that he didn't know what he was doing," he added.
Glennon had been in the Army for 21 years and had been affected by the gun suicide of a close friend.
Judge Halpin said the sergeant had "defused" the situation.