We present a side-channel attack based on remanence decay in volatile memory and show how it can be exploited effectively to launch a noninvasive cloning attack against SRAM physically unclonable functions (PUFs)—an important class of PUFs typically proposed as lightweight security primitives, which use existing memory on the underlying device. We validate our approach using SRAM PUFs instantiated on two 65-nm CMOS devices. We discuss countermeasures against our attack and propose the constructive use of remanence decay to improve the cloning resistance of SRAM PUFs. Moreover, as a further contribution of independent interest, we show how to use our evaluation results to significantly improve the performance of the recently proposed TARDIS scheme, which is based on remanence decay in SRAM memory and used as a time-keeping mechanism for low-power clockless devices.