Michael A. Garrett

The search for extraterrestrial intelligence (SETI) has traditionally framed the detection challenge with a focus on the parameter $L$ in the Drake equation - the communicative lifetime of a civilisation. I argue that the more pertinent quantity is $τ_d$, the duration during which a civilisation produces technosignatures that are \emph{actually detectable by us, now}. Modelling technological progress as an exponential process, we show that $τ_d = α^{-1}\ln(K_{\rm max}/K_{\rm min})$, where $α$ is the rate of technological acceleration and $[K_{\rm min},K_{\rm max}]$ brackets the technology levels accessible to our instruments. As $α$ increases, $τ_d$ can shrink to mere decades, dramatically narrowing the window in which civilisations overlap technically. This ``technology mismatch'' has implications for future search strategies, emphasising broadband and technology-agnostic approaches, as well as anomaly detection across multi-wavelength/messenger survey data.