We propose to observe the newly-discovered transiting planet TrES-1 during the time of secondary eclipse (when the planet passes behind the star). A successful measurement of this eclipse would constitute the first direct detection of emission from an extrasolar planet. The secondary eclipse will reveal two key quantities of the planet: its temperature (from the eclipse depth), and its orbital eccentricity (from the eclipse timing). Moreover, these observations will enable us to characterize the high-precision, rapid-cadence photometric performance of IRAC. A successful demonstration of this innovative use of IRAC would open a new observing mode for Spitzer with applications extending well beyond the study of extrasolar planets.