The doors to the office firmly locked, a frantic search for the bunch of keys with the transponder in every nook and cranny of the bag, then the realization: it's at home on the kitchen table. Does this sound familiar? While keyfobs or ID cards are often forgotten, the smartphone is almost always within reach. That’s one reason why mobile credentials — digital IDs on the smartphone — are becoming increasingly popular in modern access solutions. In this article, we explain when it makes sense to use RFID (Radio Frequency Identification) cards and when it is better to rely on smartphone-based solutions. We also take a brief look at the nature of an ideal reader/writer.