Ok,

Using an ESP01 unit programmed by an arduino sketch to auto log in to the wifi I got the ESP to publish a webpage in Chrome on the android phone that triggers an alert when the gas sensor (LPG) signal goes logic low.

All wearable running off a phone power bank. Everything boots up in about 10 seconds.

I like the webpage approach as it means anyone on the wifi can be in the loop with a simple link.

A custom app to do graphing/gps and data logging etc. is being looked at.