The possibility to use the same system for communications and short-distance radar sensing in sophisticated Internet of things (IoT) sensor nodes is given by the use of impulse-radio based ultra-wideband (IR-UWB) transceivers. An additional requirement arising from more and more sensor edge nodes in the IoT is a need for very energy-efficient low data rate communications. Zero-crossing modulation (ZXM) was proposed to enable energy-efficient receivers with 1-bit analog-to-digital converters where information is encoded in the temporal distance between zero-crossings. For low data rates we propose an IR-UWB related spike-based signaling scheme called time-derived zero-crossing modulation (TD-ZXM). A first comparison with ZXM is made in terms of bandwidth and data rate. The results show an improved energy efficiency for TD-ZXM at low data rates if bandwidth is less restricted. To achieve the same data rate for a given energy efficiency, TD-ZXM requires 3.5 times the bandwidth of ZXM, however enabling joint communication and sensing.