Two bombings on Saturday in a Cairo suburb killed a teenager and her mother, officials said, the latest in a wave of blasts to hit the Egyptian capital this week.
Militants have stepped up attacks after the army ousted Islamist president Mohamed Morsi in July 2013 and amid a deadly crackdown by authorities on his supporters.
The makeshift bombs planted in a telecommunications being built in the October 6 suburb were detonated by a mobile phone signal at around 9:00 am (0700 GMT), a police investigator told AFP.
Medics said the watchman's wife and 18-year-old daughter were killed.
Residents said the powerful blast rattled windows in nearby buildings.
Saturday's explosion comes after five makeshift bombs at four Cairo metro stations on Wednesday and a sixth at a courthouse wounded six people.
Signup to our newsletter and follow us on Facebook and Twitter!
The authorities have blamed Morsi's Muslim Brotherhood for attacks rocking the country, most of which have targeted security forces, and have blacklisted the Islamist movement as a terrorist organisation.
Since Morsi's ouster, a crackdown on his supporters has left more than 1,400 people dead and seen at least 15,000 jailed.
Hundreds have also been sentenced to death.
An Al-Qaeda-inspired jihadist group based in the Sinai Peninsula, Ansar Beit al-Maqdis (Partisans of Jerusalem), has claimed some of the deadliest attacks on security forces, as well as a failed attempt to assassinate the interior minister in September.
A little-known jihadist group, Ajnad Misr (Soldiers of Egypt), has also said it was behind a string of attacks on police in Cairo.
The government says the militants have killed about 500 people, most of them security personnel.