Ancient technology that nobody apparently uses anymore but I bought a (used) Garmin GPS (the old one was getting quite slow and took time to position). If using official maps (which I didn't for Malaysia, Laos and Tunisia), it has a nice (optional) feature of visually and aurally indicating upcoming speed zone changes, as well as over-speed alerts. Of course only as good as the data as it still has incorrect speed limits despite updated maps.

At least the OP didn't get the car impounded for excessive speeding. Happens where I am which could be very costly for excess rental and recovery fees, let alone the fine, impound and towing ones.