WSDCAM 113dB Loud Anti Theft Vibration Sensor Alarm Systems for Electric Bike Motorcycle Golf Car Trailer Mailbox Garage Door Waterproof Home Security Bike Accessories Bike Alarm with Remote

I fold my Brompton entirely or put it in “cart mode” and take it with me everywhere. No lock is sufficient but if you must lock, I also suggest hiding an AirTag and mounting an alarm like this.