Yes ! You can have as many devices as you want, and all of them can be paired with the same smartphone. All of your devices will appear in one list in the Monimoto app (see picture below).
Also let's take this example:
Bruno has an adventure bike that he travels with and a cafe racer that he built himself. He bought two Monimoto devices and put each one of them into one of his vehicles to protect them. Given that he is the only owner of two vehicles, he can pair all of his devices with his smartphone and only one of the KEYs (yes, you can use a single KEY for all your devices). Then, whichever vehicle he is using - both devices are ready to report a theft in case it occurs. Bruno will receive all notifications in one place.