Omnidirectional wireless distance measurement (No ultrasound or IR)

Help Please Omnidirectional wireless distance limiting(No ultrasound or IR)

First off hi, I'm new to the boards. I'm trying to wrap my head around what I thought would be a relatively simple project but can't seem to find a viable solution. Here are the details lets see what you guys can come up with.

An object needs to remain with a certain distance of a fixed point. If it travels beyond this distance an alarm is to be triggered.
The range is up to 30m and needs to be controllable down to 1m.
This will be outdoors, in open space but not "controllable space" IE no overhead cameras.
Both transmitter and receiver need to be omnidirectional as they may not always be facing each other.
Ultrasound cannot be used.
The circuitry on the moving object needs to be < 8in3 or so in size. The smaller the better.
Circuitry on the fixed point can be larger but preferably not much.

I was thinking of using RSSI to do it and just have the "alarm range" adjusted as the situation required. The distance is too low to reliably use RF pings as distance I think and ultrasound is out due to not being omnidirectional. Hope you guys can help.

Does pretty much everything you want but is not user adjustable in terms of distance, **broken link removed**

How about radar?

Look at this module. Output is frequency.

Make it omnidirectional by spinning the module.

Boncuk

jimlovell777 said:

Does pretty much everything you want but is not user adjustable in terms of distance, **broken link removed**

Click to expand...

Sounds pretty close to ideal other than adjustablitiy which might be able to be changed with gain on an antenna or something. Guess I've to buy one and see whats in there to make it work.

If both mobile and fixed stations have synchronized clocks (as in radio linked) the mobile unit can emit a sonic 'click' -which is not ultrasound- every second.
The fixed unit will measure the time delay to hear the beep reaching its microphone and calculate the distance as the sound travels at a known 340m/s

Optically : Barcode stickers on the mobile unit could be sensed by a rotary scanner in the fixed unit. Varying the focusing lensing on the scanner, it will read only the barcodes that are at a certain distance, also capable of detecting its relative orientation.

Or:
AG-RADAR Proximity Sensor (add to GF200/200PAlarm): BIKEBONE
**broken link removed**

Or:
For sure there is optical surveying equipment capable of telling precise distance to a target.
Amazon.com: Bosch DLR165K Laser Distance Measuring Device: Home Improvement

But... Is there other moving or not bodies in the same area ?

Miguel