Three people escaped injury when a blast bomb exploded at their house in the Village area of south Belfast early this morning.
The couple and their five-year-old grandson were treated at the scene for shock.
A Police Service of Northern Ireland spokesman said the device was thrown through a downstairs window around 2.30am. It consisted of a large firework with bolts and caused damage to the walls and furniture of the house at Monarch Street.
British army bomb experts were called in to deal with the device.