The timey-wimey detector was a makeshift device used for detecting temporal anomalies by the Doctor. He used it when he was trapped in 1969 by the Weeping Angels to detect others who had been sent backwards in time. Its outward appearance resembled a late-20th century portable open-reel tape recorder, with only one spool. It alerted the Doctor to an anomaly by dinging.
The exact nature of the device's functioning was not made clear, as the Doctor's deliberately vague explanation to Billy Shipton was that "It goes 'ding' when there's stuff." However, it may be inferred that the Timey-Wimey detector was primed to detect residual artron energy acquired by beings who had travelled in the Time Vortex. This energy was loosely described by the Doctor as "wibbly-wobbly, timey-wimey stuff", hence the name of the device.
The timey-wimey detector had one main side-effect - it automatically boiled any eggs in a distance of thirty paces. Because of this, the Doctor learnt to stay away from chickens, as "it's not pretty when they blow". (DW: Blink)