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could some one explain me these technologies? I understand the main difference is the strenght of the signal. If im trying to automatically send an alert to any smartphone (able to receibe it) can i use any of this trchnology tags? Example: imagine i have a tag in my house entrance and every time i arrive i receive a "welcome home" message in my phone. Is that possible? Or i need a trigger from my phone?

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closed as too broad by Keelan, Daniel Grillo, Phil Frost, Olin Lathrop, Adam Lawrence Oct 26 '14 at 4:41

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ I was on the fence about whether to close this question as being too broad or let it stand since it is possible to get some good information in a answer. However, the gross sloppiness of the question made the difference. That level of disrespect shouldn't be rewarded here. Screw this. \$\endgroup\$ – Olin Lathrop Oct 24 '14 at 15:42
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Well, as you say; there is a difference in range. With an RFID pulse, you could trigger something from a distance, but not your phone. Your phone needs to support RFID and I don't know of any phones that does. I guess the reasoning behind that is that RFID only supports one-way communication. Like when passing a toll-station with your car, the cars RFID tag is read by the reader equipment placed in the toll-station.

With the evolving NFC technology you may pass information in both directions. Say you are shopping for groceries, you may now tap your phone to the payment terminal which tells the phone how much you have to pay. Now the user may select an appropriate account for the transaction and give the terminal this information.

NFC also supports "tags", which is a one way communication unit. You may have a tag at your entrance and tap your phone on this. An application reads this on your phone and issue a pre-defined action. This has endless possibilites, as your app can for example tell your WiFi connected house to turn on the lamps when entering the door. But as mentioned, this requires close proximity communication.

Another possibility is to use the emerging Bluetooth Smart technology. Have you heard of beacons? They are small, very portable battery driven devices that may last for years, sending a signal of its presence every 2 seconds or so. This signal can be picked up by your phone usually at ~50 meters. An app that runs in the background can then greet you welcome, change your phone settings (silence, sound etc). Nordic Semiconductor has made a small, cheap reference design for this that you can play with. They also have an app for Android that does what you want it to do.

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