How to measure whether a smartphone is inside a 5 meter range?

[MartijnNL]

Hi there,

As currently work for company that builds mobile apps I am looking into a way to measure whether a smartphone is outside a 5 meter range. As I am not an engineer I hope your expertise can help me out in order to come up with a right direction for further research. NFC, RFID, GPS, orthogonal coils, wifi ? I don't know where to begin :)

Considerations:
- Solution should be affordable (B2C) and scalable
- 5 meter ranges should also be accurately determined through 1 or 2 normal size walls
- Sender and receiver could be anything

Application:
This solution will be used for a client that want to use people's smartphones to automatically block scooter usage. I know smart car keys do something similar, can we use this technology in a phone?

Hope this is something you guys can have a thought about!? Thanks in advance!

 

[anorlunda]

Welcome to PF.

Google "smartphone proximity sensor". Most of them use IR light which won't work through walls. But some are ultrasonic.

Here is one that sounds close to your goal
http://www.makeuseof.com/tag/auto-locking-office-door-smartphone-proximity-sensor/

By the way, I would want it to unlock my scooter only if there were no walls in the way. You don't want someone stealing the scooter when while you sit inside.

 

[BvU]

Life is getting more complicated: crooks now get scooters for free when they steal your phone...

 

[sophiecentaur]

Why not just require a password (/fingerprint code) for your mobile to unlock the scooter? That would not involve any special knowledge of RF and Engineering.
You may be wanting more than that, though. You seem to want the phone to activate the scooter automatically. The scooter could be arranged to require a very high signal level but anyone pinching the phone would automatically get the scooter, as BvU pointed out. You must have a personal key (software or hardware) if you want security.
Imo, car remote keys operate over far too great a distance and anyone who picks up a lost key can see hundreds of cars in a car park and find the appropriate car with no problem; it flashes its lights at you. There is seldom any need for the key to work before you are within a very short distance of the vehicle. When your memory starts to give you a problem (mea culpa) you can always put a map pin on Google Maps. My phone actually informs me that I have parked my car and where to find it - I never asked it to!

 

[anorlunda]

I like the idea. Think of two factor identification to log into a web site. Require both a key and presence of the phone to start the scooter. A third factor could be someone of the correct weight (plus minus a kilo or two) on the seat.

That are a measure of theft protection km but reduces the reliability of the cycle. I'll never forget some advice from a DEC security manual.

The primary purpose of system security is to assure that the system fulfills it's mission. Security that thwarts legitimate users in addition to intruders is worse than no security.

 

[sophiecentaur]

People used to use socking great chains and factory gate type padlocks. Handy for swinging round the head when threatened by thugs.

 

[MartijnNL]

Thanks so much guys for the divers ;) but valuable insights. Bluetooth might be the way to go, what do you reckon 'out of range' would be distance wise? Any way I would be able to get close to like a 5 meter range (no walls this time, anorlunda you are right :) ). But we also don't want like the lock to be activated when I'm already 10m away. Doesn't feel like a secure distance.

 

[sophiecentaur]

If you can accept up to 5m measurement range, uncluttered, then you could use a sound transponder. Send an blip and the scooter replies with a blip. The (minimum measured) delay would give you the distance and your remote key can then tell the scooter to unlock. Audio circuitry is far less hassle than RF. The timings are much easier and it is possible to have a code that would punch through any local sound interference.

 

[anorlunda]

We are talking about theft prevention, not remote start, correct?

A 5m range for scooter theft protection makes no sense. Why not 1m or even 30cm, requiring the owner to be sitting on the seat before the key ignition is enabled? It might be hard with bluetooth to exclude signals more than 1m away. Sonic signals for very short signals would be better. Ultrasonics could do that while not being audible to humans.

 

[sophiecentaur]

We are talking about theft prevention, not remote start, correct?

A 5m range for scooter theft protection makes no sense. Why not 1m or even 30cm, requiring the owner to be sitting on the seat before the key ignition is enabled? It might be hard with bluetooth to exclude signals more than 1m away. Sonic signals for very short signals would be better. Ultrasonics could do that while not being audible to humans.

Actually, pretty well anything you can think of that's non-standard will completely flummox any ordinary thief. If you have a really tasty bike then they can just hook it onto the back of a truck, having cut the chain with an angle grinder.

 

[CWatters]

I think one version of NFC is specified to 1.5 meters. Perhaps that would be ok?

However I think you need to consider some of the dangers. For example are you proposing to cut the engine when the scooter goes out of range? So what happens if your mobile phone goes flat just as you pull out of a junction into traffic? What happens if you drive past someone with a jammer?