  We present the performance of a superconducting nanowire that can be operated
in two detection modes: i) as a kinetic inductance detector (KID) or ii) as a
single-photon detector (SPD). Two superconducting nanowires developed for use
as single-photon detectors (SNSPDs) are embedded as the inductive (L) component
in resonant inductor/capacitor (LC) circuits coupled to a microwave
transmission line. The capacitors are low loss commercial chip capacitors and
limit the internal quality factor of the resonators to approximately $Q_i =
170$. The resonator quality factor, $Q_r \simeq 23$, is dominated by the
coupling to the feedline and limits the detection bandwidth to on the order of
1MHz. When operated in KID mode, the detectors are AC biased with tones at
their resonant frequencies of 45.85 and 91.81MHz. In the low-bias, standard KID
mode, a single photon produces a hot spot that does not turn an entire section
of the line normal but only increases the kinetic inductance. In the high-bias,
critical KID mode, a photon event turns a section of the line normal and the
resonance is destroyed until the normal region is dissipated. When operated as
an SPD in Geiger mode, the resonators are DC biased through cryogenic bias tees
and each photon produces a sharp voltage step followed by a ringdown signal at
the resonant frequency of the detector which is converted to a standard pulse
with an envelop detector. We show that AC biasing in the critical KID mode is
inferior to the sensitivity achieved in DC-biased SPD mode due to the small
fraction of time spent near the critical current with an AC bias.
