Following on from Part One here…
We were contacted by someone from NW Hub, who said they would try to locate our AirTag and return it to us. Excellent! With the tracking information for the parcel, they were able to ascertain the exact route it took through the labyrinthine escalator system of NW Hub. All the belts are enclosed, so it seemed likely the AirTag had come out of the Jiffy bag when it was split open, and was now underneath one of the belts resting on an inspection panel. Perhaps an engineer could remove a few panels and the AirTag would drop out?
There was also the very curious question of how the Jiffy bag came to be split open in the first place? We surmised that it had been “wooshed” through some rubber rollers at high speed, the AirTag had stuck and the envelope carried on, ripping the tag out through the end of the Jiffy bag. It turns out that’s not how it works, and letters are scanned from above with cameras, in any orientation (presumably they have to be face up) as they go along the belts. It also transpired that the small, light, Jiffy bag should not have been in NW Hub at all (!). Remember back to 25th Dec when the parcel went here before it went into NW Hub?
That is a “Mail Centre” where they pre-process the mail. Apparently, the machines at NW Hub can’t handle items lighter than 50g – they tend to fall off belts, don’t go around bends properly, etc. So the MC should have detected that and not sent it over the road to NW Hub. Where and how did the envelope get ripped, though – still a burning question!
Our contact had a CAD drawing of the machinery in the Hub as shown in the below image. They overlaid the location data we had for the AirTag onto the drawing, and with knowledge of which belts on which floor the parcel went along (from the RM tracking data), they were able to home-in on where the tag might be.
Engineers were dispatched to remove inspection panels in the section of the line the tag was most likely to be in…
But it wasn’t there.
We started doing some data analysis on the AirTag location data. There are two booleans in the location information: “isOld” and “isAccurate”. We quickly sifted out the locations that were old or inaccurate and got a smaller set of candidate points. Bear in mind (if you’ve read the blog about how the AirTag tracking network works) that you get the location of the PHONE, not the location of the tag. Moreover, if the phone was “asleep” (a slightly complicated definition of that, but either the screen is on, or has been recently), when it detected the tag, it logs the ID of the tag and the time, but does nothing else. Then later, when the phone is next looked at, it runs through the tags it’s seen while it was asleep and sends out location reports for those tags – from wherever the phone is at that time. So it could be quite far away from where the tag was actually detected.
There is a “horizontal accuracy” number, but it’s not at all clear what that means. We did think it might be based on the RSSI (Bluetooth signal strength) of the tag read, but it’s not a percentage, and hovers around 50 for most readings, sometimes going as high as 400, so we are really not sure how to deal with that piece of data. It might be the “HDOP” (Horizontal Dilution Of Precision), which has to do with GPS accuracy due to alignment angles with the satellite constellation. But it doesn’t really help us find the tag.
We took the points that seemed most plausible (i.e. took out the outliers), and worked out the centroid of these points. That gave a new location to correlate against the CAD drawing of the site and hoped that would give a better clue as to where the tag is. It didn’t help much.
Next, We decided to heat map the data points. We rounded the lat/long points at some selectable number of decimal places, using the information from this article as guidance. 5 decimal places correspond to 1.1m on the ground. As far as we can tell, the iPhone location service is accurate to somewhere between 4 (11m) and 5 (1.1m). Don’t be fooled by the apparent accuracy of seeing 13-odd digits in a lat/long value. That’s down at the sub-micron level – the scale of a virus molecule! Then we created a matrix of the offsets of the points from a fixed corner point and counted how many tag reads fell into each square. Displaying sections of this matrix allowed us to find the location most often reported.
10 marks the spot! Or does it? Remember these are the locations of the phones that spotted the AirTag, not the AirTag itself (which was why we tried the centroid approach first, hoping people would be passing the tag randomly from all sides). But of course, that’s unlikely to be the case, as there are specific areas where employees can and can’t walk around the machinery, so this “10” might be an operator’s station or something. Who knows – it’s all very frustrating.
The result of this analysis was a point 6m “N” (along the roofline of the building) from the previous estimate, so I’m hoping a search in this area will bear fruit.
If that doesn’t work, the only remaining thing (unless anyone here has any new ideas, particularly in relation to the horizontal accuracy number), is to move to what we refer to as “Plan B” – for us to visit NW Hub with a new model iPhone and make use of the UWB (Ultra Wide-Band) radio they have (which the AirTag also has) to located the tag “manually”. We don’t currently have an iPhone with the UWB technology on board (models from iPhone 11 onwards), so we are on the look-out to borrow a phone for a few days, which we can sign into as “me”, so it picks up the ownership of our AirTags, and would enable us to locate the device more accurately if we were there in the building.
It’s worth noting that the most recent release of iOS (Oct-23) includes the ability to share an AirTag with another person – this would have been ideal: We could have shared the tag’s ownership (and hence the ability to pinpoint its location) with our RM contact.
Meanwhile, as of 28-Apr, the promised cheque from the RM compensation department has not arrived yet. They said to give it 10 days (at least they’re realistic about how long it takes to deliver things by post in this country, LoL!), but it has not yet arrived. We’ll be picking that thread up next week. we think a complaint escalation might be in order.
We chased up the compensation claim and heard (17-Apr) that “a cheque was issued to you, which hopefully you have now received. If not, please let us know and we can look into this further for you.” We didn’t receive the cheque (Quelle’s surprise) so “let them know”. They confirmed “The claim was processed on 11-Apr and you will receive the outcome via letter within 5-10 working days. If you are still not in receipt of the cheque by the end of the week, please come back to us so we can make some inquiries with our finance department.” Honestly, it’s like reading those scam emails we get every day!
The end of the week came and went. We “Came back to them”. A few days later they “confirmed that a re-issued cheque has now been sent.” We’ll give them another 5-10 working days, then. What an utter shambles.
5th May letter and cheque from RM posted.
The 17th May compensation cheque arrived, was paid into the bank, and cleared successfully!
Our contact at RM eventually decided enough was enough and they were not going to continue to search for the missing AirTag in their machine.
The tag continued transmitting until 23rd May when the battery finally expired. RIP little AirTag – we’ve been through a lot together!
As a poignant footnote to this blog, in early Nov-23 it was announced that “Royal Mail loses 360-year monopoly on delivering parcels from Post Office sites“, and it was noted that “Industry sources said the decision was the result of increasing dissatisfaction at the Post Office with Royal Mail because of customers complaining about the standard of service.”
We can’t help thinking this is not unrelated 😉