startMonitoringSignificantLocationChanges not working in swift

It's working, but it's really hard to trigger significant location changes - it usually happens when the device is changing cell towers - I don't think it's possible to do with the simulator.

You'd probably have to get on a bike/car and travel AT LEAST a few kilometres.

There's a trick you can use though, that will trigger significant location change:

Switch Airplaine mode in your iPhone on and off with a few second intervals repeatedly, it should trick the device into thinking that it changed cell towers and trigger the significant location change.

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In your simulator, goto Debug->Location->Custom and change location, then test it.