theusch 
A customer has requested that we add GPS tracking to the device, which is a commercial/consumer rental device. Think "lojack" -- when not returned, or stolen, they want to be able to find the device.
I have no idea where to start. Any suggestions? Try to keep the cost down, please...
https://www.sparkfun.com/product...
sparkfun has nice small gps module, I'm sure you can find it for less from a distributor!
Jim
awit 
The GPS tracking usually use two devices: GPS receiver and GSM modem. If You don't want to use specialised device for tracking, You must read actual position from GPS and send it, periodically or in answer to received demand, by SMS to given phone number or GPRS to given internet server.
It could easy be the cheapest to have an app on a cheap cellphone that regularly send a SMS.
valusoft 
Monitoring of position within a defined perimeter can also be used to trigger tracking of a stolen item if it leaves the defined area.
For a US company: they are good at geo-fencing etc (I had a consultant job for them once when I lived in US)
clawson 
Left of field idea: Buy a $10 Android phone and strap it on. Use Android Device Manager to track it. The only "issue" is how you keep the phone charged ;-)
(this suggestion brought to you by Not Entirely Serious Productions Inc.)
gchapman The GPS tracking usually use two devices: GPS receiver and GSM modem.
LoRa is an order of magnitude less power than GSM yet still has the range and can be powered via AAA cells.
There are recent AVR plus LoRa projects on crowd funding.
LoRa's US weakness is coverage; would either need to add a private gateway or do peer-to-peer (one peer locates the other peer, one peer is mobile)
GPS - add GLONASS resulting in GNSS
http://wiki.dragino.com/index.php?title=Lora/GPS_Shield
http://wiki.dragino.com/index.php?title=Lora/GPS_HAT
clawson More seriously, When I google "combined gps and gprs module" there's a lot of promising looking hits but the one that catches my eye is SIM808 simply because simcomm2m.com kind of "own" this entire market. Adafruit have it for $30...
https://www.adafruit.com/product...
I guess one question is "how much do you want to spend?" and are there design constraints like physical size of particular power requirements? (my mad idea about an Android phone wasn't that far off the mark - GPRS consumes batteries - think how long any phone lasts in standby - so battery/power is an issue)
EDIT: actually when you explore SimCom's website it seems that 8xx units have possibly been surplanted by 9xx units like 908 and 968.
theusch Wow, a lot of responses quickly.
Not my area--wouldn't the GSM need some kind of subscription to send stuff? [now I have to learn GSM basics]
Should be able to have enough power for at least periodic updates.
Would it be "two way" to awaken to "you have been stolen" message and then start frequent updates? [now I have to learn lojack basics]
Indeed, the phone idea is interesting.
If really stolen, then wouldn't it be in a closet or similar where it is questionable whether GPS and/or GSM contact can be made?
clawson Not my area--wouldn't the GSM need some kind of subscription to send stuff?
The real solution is the Google keyword "M2M" so if you google "SIM for M2M" you should hit stuff. I think most network operators have cards/plans specifically for M2M usage.
EDIT: interesting article about M2M cards: http://www.wireless-innovation.c...
EDIT2: As "Verizon" is one of the US cell networks I've heard of I tried "Verizon m2m plan" and it hits this: https://www.verizonwireless.com/...
(can't help thinking it's a bit of a rip-off unless the customer is happy to bear the cost - you could just get a PAYG SIM with data for much less assuming the credit on it is not time limited!)
EDI3: (no more edits I promise!). So I tried AT&T and Sprint to see what they offered. They seems reticent about publishing an open figure for M2M data rates (presumably its very open to negotiation?) but I hit this very interesting page on AT&T: https://starterkit.att.com/
clawson That AT&T starter kit apparently consists of this:
http://www.nxp.com/products/soft...
which uses this:
http://www.nxp.com/products/micr...
(its an M4 but I've never heard of it!).
But of more interest perhaps is the radio board that AT&T chose to put on top. The pictures show a "WNC M14A2A" and when you google that you arrive here:
http://www.wnc.com.tw/index.php?...
The M14A2A does not appear to have GPS but the M14Q2G, M14QFG, M18Q2G, M18Q2FG appear to offer GPS.
gchapman LoRa's US weakness is coverage; would either need to add a private gateway or do peer-to-peer (one peer locates the other peer, one peer is mobile)
Pycom
Pycom and Canonical to enable LPWAN communications via snaps
Maarten Ectors (Canonical, Internet of Things)
Nov 25, 2016
https://www.pycom.io/pycom-canonical-enable-lpwan-communications-via-snaps/
...
It is possible to use for instance LoRa in a private network whereby, for example, you can have several battery operated LoPy modules connected to soil sensors in the field and a LoPy connected to a Raspberry Pi in the farm and you are able to show a real-time dashboard to the farmer. It’s super quick to set up and a very cost effective way of getting field data to mission control.
...
A LoRa node sleeps, wakes periodically to transmit, waits through two receive windows, then sleeps.
The Pycom LoPy can be either a node or a Nano-Gateway; nodes can run on AAA cells with the Nano-Gateway on AA cells.
https://www.pycom.io/support/supportdownloads/
https://www.pycom.io/wp-content/uploads/2016/09/lopySpecsheetFinal.pdf (LoPy 1.0)
Ubuntu
Ubuntu for the Internet of Things
https://www.ubuntu.com/internet-of-things
...
(mid-page)
Snaps for security
Ubuntu Core is an all-snap version of Ubuntu.
A snap is a secure, easily upgraded, universal Linux package for an app and all its dependencies. ...
...
Pycom
So why did we open source?
Nov 16, 2016
snapcraft - Snaps are universal Linux packages
via
Ubuntu
Ubuntu Core
Ubuntu Core is a tiny, transactional version of Ubuntu for IoT devices and large container deployments.
...
Edit : more on snaps and Ubuntu Core
gchapman If really stolen, then wouldn't it be in a closet or similar where it is questionable whether GPS and/or GSM contact can be made?
One can demonstrate by attempting to phone home from a closet 
But, all must come out into the daylight to play.
... or similar ...
Disklabs Digital Forensics and Data Recovery
Faraday Bags
The one linked to at AliExpress only works with 2G. I believe this is a common limitation of a lot of these cheap offerings.
But SMS on 2G (GSM) take the least amount power.
gchapman For those in the US :
AT&T 2G network shutdown
https://www.att.com/esupport/article.html?_escaped_fragment_=/wireless/KM1069631
Learn about the upcoming 2G network shutdown to be completed by the end of 2016.
...
js 
The one linked to at AliExpress only works with 2G.
I think 2G is shutting down this month, maybe even today here.
valusoft Yep today. Gone... woosh...
No 2G service left in northern Ohio.
We had to pay through the nose to update all of the cardiac monitors in the county so they could still transmit their 12-lead EKG's to the ER's.
Did that earlier this year.
I purchased this little, inexpensive, GPS with its built-in patch antenna for $15 from SFE and it works great.
https://www.sparkfun.com/products/13740
(I've purchased, over the years, plenty of other GPS modules that cost many times that.)
If the customer is using Pelican boxes for their product then obviously the box is a Faraday cage, and you would need a GPS with an external antenna connection, cable with the correct connector, and antenna.
You also would need to know if the antenna was powered or not, and it the GPS module was set up to power the powered antenna or not.
The antenna cable and antenna can cost more than the GPS module, hence the popularity of the GPS modules with the built-in patch antennas.
Remember, you get a 2 dB loss per connector, (or whatever, I don't recall), and for weak GPS signals you can't afford lots of transmission line losses, so no connectors mounted on the box wall / truck's roof, etc. You want only one cable with one connector on each end, not a patch work Hodge podge.
Know that many GPS modules have a watch battery so that they can store the GPS ephemeris and almanac data, which, depending on the time since the GPS last was powered up and had a lock, can shorten the time to first fix, (Time to GPS lock).
Lots more info about the intended usage is needed, (size, antenna options, power supply options, expected locations and hence GPS coverage, tech know how of the thief, (i.e. their ability to recognize and either jam or disable the GPS or the data modem, etc.).
Interesting project!
JC
valusoft Pelican boxes in my experience are plastic... tough plastic.
The polyethylene might be lossy at microwave frequencies and you don't need much loss to upset GNSS.(gps isn't the only player in town these days)
I don't think the black cases are conductive.
If really stolen, then wouldn't it be in a closet or similar where it is questionable whether GPS and/or GSM contact can be made?
Several years ago I put a gsm into a metal cookie jar, closed the lid, and phoned it.
It rung.
valusoft Aaah, the power of good Dutch biscuits!
I have tried to call from a radio dead room and it worked !
When we then plunged the two holes where the wires go in and out it died.
js call from a radio dead room and it worked !
Did you get in contact with ghosts?? 
gchapman It could easy be the cheapest to have an app on a cheap cellphone that regularly send a SMS.
Technical Specifications for TrackR
https://thetrackr.co/tech-specs
...
The TrackR is a Bluetooth device that connects to an app running on your phone.
...
Crowd GPS
...
When the signal (Bluetooth Smart with unique identifier) is detected, the phone records the current GPS location, sends a message to the TrackR server, and the TrackR server will then update the item's last known location in its database.
...
via an advertisement
http://www.studylifestyle.com/2016/trackr/1f/
