Using your iPhone, you can ask Siri to record your traffic stop. First, you need to install and configure the shortcut: POLICE. When you see the blinking lights, say the given phrase. The program then pauses any music, turns down the iPhone brightness, and puts the phone into Do Not Disturb mode.
It then sends a quick text to your preferred contact and starts recording using iPhone's front-facing camera. The recording can be emailed to a contact or saved to Dropbox, according to Schneier on Security.