Three men were arrested by police in County Donegal in the Republic of Ireland on Thursday morning.
A fourth man, a 27-year-old, was detained by the PSNI on Thursday night.
The couple who live in the house are both PSNI officers and were at home at the time. Police said the attack was a "clear attempt to murder" officers.
The man arrested by the PSNI has been taken to Antrim police station for questioning.
The device was discovered at Glenrandel in Eglinton in the early hours of Thursday morning and fifteen houses were evacuated.
Four men are still being questioned by police after a bomb was found under a PSNI officer's car outside his house in Eglinton, near Londonderry.