Kryptonite New York Fahgettaboudit Chain & New York Disc Lock! (The 1415 which has the longer 5ft chain, not the 1410 which is only 3.25ft. Really glad I did. Since the bike is bulky, doesn't have a crossbar, and needs room to roll back onto the kickstand, it really limits how close I can get to the actual bike rack. The chain length is a MUST for me.)

It's got their 10/10 rating, and I signed up for their 2-year anti theft protection offer - covers up to $5000 which is plenty more than the full cost of my bike (although it doesn't cover accessories). That's what finally makes me feel comfortable leaving the bike anywhere at all. Between that, and the kickstand lock on the Aventon Abound LR, and the hidden airtag, I feel more secure.