Puck.js for asset tracking

The code would look something like this. Just tested and it works fine - you'd just want to choose how you filter out the beacon you're interested in (name, manufacturer data, etc):

function updateAdvertising(device) {
  var data = new Uint8Array(7);
  // our data - all 0 for nothing, 
  // or RSSI + 6 bytes address
  if (device) {
    data[0] = device.rssi;
    var addrAsBytes = device.id.substr(0,17).split(":").map(x=>parseInt(x,16));
    data.set(addrAsBytes, 1);
  }
  
  NRF.setAdvertising({},{ 
    showName:false, 
    manufacturer: 0x0590,
    manufacturerData: data
  });
}

function scanForDevice() {
  NRF.requestDevice({ 
    filters: [{ name: 'Puck.js 5a47' }], 
    timeout: 2000}).then(function(device) {
    updateAdvertising(device); // found
  }).catch(function(err) {
    updateAdvertising(undefined); // not found
  });
}

setInterval(scanForDevice, 60*1000); // scan once a minute

In terms of gateways, I'd suggest just using something like a Raspberry Pi 3 as a start, and then you're totally flexible (you could move to any Linux-based gateway later on if you wanted). What did you want to bridge it to? WiFi, Ethernet, GSM?

I believe Rigado do some good professional Gateway hardware if you wanted something that 'just worked' though: https://www.rigado.com/cascade-gateway/

It's also possible to use a Pixl.js (http://www.espruino.com/Pixl.js) with a shield for ethernet/wifi/gsm if you want to stick with Espruino for everything.

To buy Pucks I'd just order them direct from me at https://shop.espruino.com/puckjs - you should usually get them in Germany in 3-5 days.