Assertions have long been used to validate the functionality of software systems. Researchers and practitioners have extended them for validation of non-functional requirements, such as performance. This paper presents the implementation and application of the performance assertions in mobile device software. When applying performance assertions for such systems, we have discovered and resolved a number of issues in assertion specification, matching, and evaluation that were unresolved in previous research. The paper describes a simple, but effective framework geared towards mobile devices that allows specification and validation of real world performance requirements. Categories and Subject Descriptors D.2.4 [Software Engineering]: Software/Program Verification; C.4 [Performance of Systems]. General Terms Measurement, Performance, Verification. Keywords Mobile devices, assertions, performance.