Almost all Concept 2 rowing machines can be upgraded to a PM5 monitor with Bluetooth, which is what is required to connect to asensei. Older models of Concept2 rowing machines may have a PM3 or a PM4 rather than a bluetooth equipped PM5 and these can be upgraded. While it is possible to connect these older devices to smartphones and tablets using cables, the asensei app does not currently support any connector cables for reasons that we explain below.
Currently we recommend that users upgrade their PM3 or PM4 to a PM5 which supports Bluetooth connection smartphones. This is generally a pretty straightforward process and you may even be able to sell your PM3 or PM4 once you've done so, reducing the cost of the upgrade, which at the time of writing is around $180 (US). For more information about how to retrofit a PM5 please see this article from Concept 2.