  We have developed novel instrumentation for making Lagrangian measurements of
temperature in diverse fluid flows. A small neutrally buoyant capsule is
equipped with on-board electronics which measure temperature and transmit the
data via a wireless radio frequency link to a desktop computer. The device has
80 dB dynamic range, resolving milli-Kelvin changes in temperature with up to
100 ms sampling time. The capabilities of these "smart particles" are
demonstrated in turbulent thermal convection in water. We measure temperature
variations as the particle is advected by the convective motion, and analyse
its statistics. Additional use of cameras allow us to track the particle
position and to report here the first direct measurement of Lagrangian heat
flux transfer in Rayleigh-B{\'e}nard convection. The device shows promise for
opening new research in a broad variety of fluid systems.
