A quick bug-fix beta release (Thank you Damian for reporting it!) – if you have an incompatible version of the watch app installed it will now pop up a friendly-ish message asking you to upgrade the watch app, rather than crashing with an obscure error.
Available on for beta testing here: https://play.google.com/apps/testing/uk.org.openseizuredetector
Sorry for the inconvenience again!