The Nest is a photoelectric smoke sensor. The Kidde is an ionization sensor.
"Kidde strongly recommends that both ionization and photoelectric smoke alarms be installed to help insure maximum detection of the various types of fires that can occur within the home."
"Kidde strongly recommends that both ionization and photoelectric smoke alarms be installed to help insure maximum detection of the various types of fires that can occur within the home."
More info: http://consumerist.com/2010/08/25/fire-chief-most-smoke-alar...