Every transmission tells the opponent that you are there, and often where. EMCON means deliberately choosing when to transmit and when to stay silent.
In practiceWarships sail with their radars switched off and listen passively only, so as not to be detected; land units restrict radio traffic before an attack; drone pilots keep their transmissions as short as possible. Silence does cost information: it is always a trade-off between seeing and being seen.
EMCON (Emission Control) is the deliberate control of your own emissions — up to and including complete radio silence — to limit detection by enemy ESM (EW: Electronic Support Measures). It is the constant trade-off between “seeing” (switching your sensors on and gaining information) and “being seen” (giving away your position and intentions). Every transmission is a risk.
EMCON recurs throughout this course: the operator's dilemma with anti-radiation missiles (SEAD & DEAD), a radar's choice whether or not to transmit, and the vulnerability of active seekers in the terminal phase (Missile Guidance). It is in fact the strategic side of LPI/LPD (Radar, New concepts in EW).