  We propose a single photon detector based on a superconducting quantum
interference device (SQUID) with superconductor-normal metal-superconductor
Josephson weak links. One of the two Josephson junctions is connected to an
antenna, and is heated when a photon is absorbed. The increase of the weak link
temperature exponentially suppresses the Josephson critical current thereby
inducing an asymmetry in the SQUID. This generates a voltage pulse across the
SQUID that can be measured with a threshold detector. Realized with realistic
parameters the device can be used as a single photon detector, and as a
calorimeter since it is able to discriminate photons frequency above $5~$THz
with a signal-to-noise ratio larger than $20$. The detector performance are
robust with respect to working temperatures between $0.1~$ K and $0.5~$K, and
thermal noise perturbation.
