Lost in the mail
A new postal probe can pinpoint hold-ups
The porters at Trinity College, Cambridge, were puzzled by the faded hand-written letter. They did not know the person it was addressed to. Inside was a note which appeared to suggest a meeting; perhaps even a date. But that meeting probably never took place. The letter had been posted in March 1950 and had been lost in the mail for 56 years.
It is unusual for letters to go walkabout for that long, but unexplained delays of a day or two are common. Postmarks can sometimes provide a clue about where the hold-up occurred. Usually, though, a lot of guesswork is involved. When post offices try to improve their service they sometimes send an electronic probe through the mail. This typically consists of a small motion sensor which records the time of day whenever the letter containing it is moved. This can show that a letter might have languished somewhere for hours, but exactly where that was may remain a matter of conjecture.
The GPS Letter Logger should change this. It is a device that uses the satellite-based Global Positioning System to find out exactly where it is. The probe takes advantage of the way that the electronic circuitry needed to build a GPS receiver has shrunk in recent years. Not only is that good in itself, it also means the equipment needs less power, and hence the batteries can be smaller as well. Small GPS trackers of this sort are already used to locate things like delivery trucks, and to find objects that have been stolen, such as cars and high-value consumer products. But a bit of modification was needed to build one thin enough to fit into an envelope and then withstand being stuffed into sacks, thrown into delivery vans and run through automated sorting systems that shuffle letters at the rate of 12 a second.
Usually, a GPS tracker transmits its position using a radio or mobile phone connection. The US Post Office did not require this, in part because mail often travels in aircraft, and transmitting devices are supposed to be switched off during take-off and landing. Not having to transmit also helped to keep the Mail Logger small.
The Letter Logger was developed by TrackingTheWorld, a company based in Burlingame, California. To travel undetected in the guise of a standard business letter, the device needed to fit into the most commonly used envelope (a number ten in America, which is about 100mm by 240mm). It had to contain no part thicker than a quarter of an inch (6.4mm) and be capable of a little bending. To complicate things, it also had to work in the vertical position, which is how letters travel in automated sorters. This means the circuit board would be edge-on to the sky, the worst position to pick up the satellite signals needed to triangulate its position. Moreover, the device needed to be capable of doing all this while inside buildings and vehicles.
The Letter Logger can be programmed to check its position every few minutes, over longer intervals, or only when an in-built motion detector senses movement, says Jude Daggett, of TrackingTheWorld. The journey log is stored on a standard micro-SD card to make it simple to use without any special software. This allows the log to be read by a laptop computer and displayed as a journey on Google Earth. The inability to transmit does not greatly detract from its usefulness: if the probe’s log showed, for instance, that the envelope it was inside crawled along Interstate 405 before turning off to Los Angeles International Airport where, after a short delay, it suddenly zoomed off to Phoenix Sky Harbour, then it most probably went airmail.
But if it disappeared for half a century, unfortunately even future supercomputers would not be able to work out where it had been. If the probe is not delivered within a week or so, its battery goes flat.
