The recent increase in demand within the wireless user community for short-range, very high rate data transmission (data, video) devices has spurred the growth of a new generation of 4G devices, viz. ultra-wideband (UWB). Due to its wide band of operation (3.1-10.6GHz) and non-conventional transmit/receive scheme (using short-duration, narrow baseband pulses), spectral power leakage to outside frequency bands causes interference with other wireless standards. In this paper, we focus on 'out-of-band' interference testing of UWB devices during production test. Due to stringent FCC spectrum regulations and very low power spectral density levels of the associated signals (-41.3dBm/MHz), production testing for interference is a big challenge and can incur significant test time, resulting in increased test cost. We propose a simple, low-cost test methodology for testing UWB devices. Simulation results are presented for a typical home environment. The channel model used can be easily modified and incorporated in any production test environment. Results show that using simple tests, estimates of 'out-of-band' interference can be obtained easily using the proposed test methodology.