A recent NERC-funded proof of concept award successfully demonstrated that Global Navigation Satellite System (GNSS) signals reflected off the sea surface and received by very low cost (<£30) GPS receivers can be used to estimate the difference in height between the receiver and the water. This represents a method of remotely sensing tidal elevations and, if averaged over time, mean sea level. These could be routinely and remotely measuring sea level at a cost that would allow unprecedented numbers of systems to be deployed around the world by organisations of all sizes and levels of funding. Here we propose to take the initial proof of concept from TRL 3 up to TRL 7 by designing a self-contained unit that receives, records and processes the required signals to output a tidal water level in near real time and at a target hardware and assembly cost of less than £100. The demonstration units will be tested and used by our project partners, the RNLI, initially to provide tidal information at an intertidal causeway with a history of RNLI rescues of members of the public who have become stranded by the rising tide. The technology has the potential to be rolled out not only across the UK but globally, potentially as open source designs & firmware, revolutionising the ability to collect tidal and sea level data at an unprecedented price point and operational simplicity.