https://devzone.nordicsemi.com/f/nordic-q-a/40624/how-to-synchronize-a-ble-observer-with-my-applicationExamples in SDK15 use the Observer pattern to handle BLE events (using the macro NRF_SDH_BLE_OBSERVER). AFAIK, the registered handler runs in some IRQ context, typically higher then my main context. Looking at the experimental ble_app_interactive exampleen-USTelligent Community 13Wed, 21 Nov 2018 13:31:23 GMThttps://devzone.nordicsemi.com/thread/158425?ContentTypeID=1Wed, 21 Nov 2018 13:31:23 GMT137ad170-7792-4731-bb38-c0d22fbe4515:eb8c3948-e985-4c73-b7da-46479b7a62b3Sigurd<p>Hi,</p> [quote user=""]Is the code in the example valid, or should access to <em>m_device</em> be synchronized?[/quote] <p>&nbsp;It&#39;s valid. You don&#39;t need any synchronization.</p> [quote user=""]AFAIK, the registered handler runs in some IRQ context, typically higher then my main context.[/quote] <p>Correct, Softdevice event handler(SD_EVT_IRQn/SD_EVT_IRQHandler) runs at&nbsp;interrupt priority level 6. This is also the same level as the&nbsp;<span>app_timer. So they will not&nbsp;preempt&nbsp;each other. (Note that in SDK 15.0 the interrupt priority level for both are set to 7, but set to 6 for both in SDK 15.2)</span></p><div style="clear:both;"></div>