  Ultra-high energy cosmic rays (UHECRs), whose energy are beyond
$10^{18}~\mathrm{eV}$, are the most energetic particles we have ever detected.
The latest results seem to indicate a heavier composition at the highest
energies, complicating the search for their origins. Due to the limited number
of UHECR events, we need to build an instrument with an order of magnitude
larger effective-exposure to collect UHECRs in future decades. The Fluorescence
detector Array of Single-pixel Telescopes (FAST) is a proposed low-cost, easily
deployable UHECR detector suitable for a future ground array. It is essential
to validate the telescope design and autonomous observational techniques using
prototypes located in both hemispheres. Here we report on the current status of
observations, recent performance results of prototypes, and developments
towards a future mini-array.
