A combination of radar and video, the system can detect small flying objects such as drones, model aircraft and balloons, as well as objects bigger than seven centimetres that are thrown in from outside the prison, Aargau's home affairs department said in a statement.
The new system will be operational next spring and will “serve to alert staff in a timely manner so they can take appropriate measures”, authorities said.
Prison bosses rejected another system that could interfere electronically with drones, since that would require constant updating, which would be costly.
To date no attempts have been made to smuggle items to prisoners at Lenzburg by drone, but cases have been reported in other prisons in Switzerland.
In August the detention centre in Pöschwies, in the canton of Zurich, said there had been two attempts to fly drones over the prison.
And a prison in Menzingen, in the canton of Zug, is also looking to install a drone detection system following a successful attempt to deliver a mobile phone to an inmate via drone.
Smaller prisons in the country have considered putting nets over their exercise yards to protect against drones, but that solution is criticized by animal protection groups over fears it could be harmful to birds.