I bought an Invoxia GPS tracker for my e-bike. It's small enough to secrete inside the frame, battery should last a month before re-charge. You can set up zones so that you are alerted on your phone if it the tracker leaves that zone. It cost just under €100, and does not require a sim card or a monthly subscription for the first 3 years. After 3 years, it's €10/year.

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Giles. Mogless in Paris.