oruxmap works great with my heart rate monitor:
http://www.amazon.it/gp/product/B00A2PACME/ref=oh_details_o05_s00_i00?ie=UTF8&psc=1
but sometimes it happens that i go a little far away from my bike where i leave my smatphone and so i lost signal (smart bt range is very low). if i forget to check my sensor i finish the trip without record heart rate cause sensore switch off in 10-15 seconds if it loses signal.
so an altert for lost signal , like lose gps external it could be very useful fo me.
best reguards, thanks for your hard work! ;)