  We present a detailed analysis of the bright Cepheid-type variable star V1154
Cygni using 4 years of continuous observations by the Kepler space telescope.
We detected 28 frequencies using standard Fourier transform method.We
identified modulation of the main pulsation frequency and its harmonics with a
period of ~159 d. This modulation is also present in the Fourier parameters of
the light curve and the O-C diagram. We detected another modulation with a
period of about 1160 d. The star also shows significant power in the
low-frequency region that we identified as granulation noise. The effective
timescale of the granulation agrees with the extrapolated scalings of red giant
stars. Non-detection of solar-like oscillations indicates that the pulsation
inhibits other oscillations. We obtained new radial velocity observations which
are in a perfect agreement with previous years data, suggesting that there is
no high mass star companion of V1154 Cygni. Finally, we discuss the possible
origin of the detected frequency modulations.
