Abstract: Radio observations are a versatile probe for potential dark matter interactions. In this talk, I will present two complementary approaches to searching for dark matter using radio signals.

First, I will discuss how we can use the pre-reionization universe as a pristine calorimeter for energy injections from decaying or annihilating dark matter to primordial black holes. As these injection sources are inherently inhomogeneous, with energy deposition often prolonged and non-local, I will present our simulation framework, DM21cm, that addresses these challenges, and forecast the impacts on the 21-cm power spectrum observables.

Second, I will turn to the ultralight end of the dark matter spectrum and discuss axion echoes -- decay photons produced when background radio fluxes stimulate the decay of axion dark matter, traveling back toward the stimulating source. Bright galactic radio sources such as supernova remnants and diffuse synchrotron radiation can induce observable echoes, enabling single-dish and drift-scan telescopes to probe competitive regions of axion parameter space. I will explain the echo geometry and our observation strategies, and, time permitting, discuss recent work on detecting echoes of solar radio emissions from axion stars.