The Army bomb disposal team was called out three times overnight after separate suspicious devices were discovered in Dundalk and Dublin.
In the first incident, Gardaí alerted the team to Castle Heights in Dundalk after an explosive device was found under a car at approximately 2.30am.
The team dismantled it and the all-clear was given just before 4am.
The same team then went to Glengowan in Dundalk where a device had earlier exploded at a house.
No one was injured and the all-clear was given at 4.30am.
In Dublin, a suspicious device found outside a house in Crumlin after 9pm was declared a hoax by the bomb disposal team.