Connect to a MI FlowerCare sensor

Finally some success

var currentSevice = false;

function getData() {
  var gatt;
  NRF.connect("C4:7C:8D:62:0D:5A").then(function(g) {
    gatt = g;
    return gatt.getPrimaryService("00001204-0000-1000-8000-00805f9b34fb");
  })
  .then(function(service) {
    currentService = service;
    return service.getCharacteristic("00001a00-0000-1000-8000-00805f9b34fb");
 })
 .then(function(characteristic) {
     return characteristic.writeValue([0xa0, 0x1f]);
 })
 .then(() => {
     return currentService.getCharacteristic("00001a01-0000-1000-8000-00805f9b34fb");
 })
 .then((characteristic) => {
    return characteristic.readValue();
 })
 .then(function(value) {
   console.log(value);
   gatt.disconnect();
   console.log("Done!");
 })
   .catch(function(error){
     console.log("error", error);
   });
}

setWatch(function() {
  getData();
}, BTN, { repeat:true, edge:"rising", debounce:50 });

Output

DataView {
  "buffer": new ArrayBuffer([207, 0, 0, 209, 12, 0, 0, 24, 124, 1, 2, 60, 0, 251, 52, 155])
   }

Next is to format the values but I save that for this weekend :)