To deliver real world cryptographic applications, we are increasingly reliant on security guarantees from both the underlying mathematics and physical implementation. The micro-processors that execute such applications are often designed with a focus on performance, area or power consumption. This strategy neglects physical security, a fact that has recently been exploited by a new breed of micro-architectural side-channel attacks. We introduce a new attack within this class which targets the use of low power cache memories. Although such caches offer an attractive compromise between performance and power consumption within mobile computing devices, we show that they permit attack where a more considered design strategy would not.