RTL 510. Why can I not connect it to my phone or any other app? Is this planned so that I have to purchase a newer device? Why cant it use ant+ with a android phone that has it built in?

The RTL510 is an older model & phone connection was never a feature of the RTL510. I doubt it will be implemented.

To have phone connectivity you would need to buy the newer  RTL515

Ok.  So you are confirming that there is no reason that it should not work.  Garmin has just chosen for it not to work.  Cool

I never said that.

.fallingrock is correct, the RTL510 only has ANT+ not BTLE

In theory the RTL510 could work with phones that have ANT+ connectivity. Most recent phones don't have ANT+, but still some do. It is only a matter of providing an app that would talk with the RTL510 over ANT+. Garmin doesn't provide one for numerous reasons, but I believe the radar ANT+ profile is publicly available, so anyone with appropriate skill could make an app.

Many android phones have ant+ built in.  All samsung phones do.  Really not hard to code it if Garmin wanted to.

Unfortunately with the prevalence of BTLE less & less manufacturers are supporting ANT+ in their phones & according to the ANt Directory of supported devices, Samsung hasn't supported ANT+ on its phones after the S20.

Maybe it could be done but with a diminishing user base it makes no sense for Garmin to divert engineering effort into doing this when they already have a product that does it over BTLE

True.....  Also why should I ever buy another garmin product then.  It makes no sense at all to divert my income generating effort to Garmin when it wont support a product I purchased fairly recently.  I am not a fan of planned replacement theory.  And seriously....  Someone could have it coded in a day as they already have the code from previous devices. Its an ANT+ standard that they own.

Brilliant answer and I thank you for your input.  However the rtl510 is a ANT + device.  Samsung phones for example have ANT+ built in natively.  

If garmin builds an app to allow phones to work on ble then it would not be an issue for a billion dollar company to add ant+ at the same time. I am sure the coding has already been done for other products and devices and it would be a simple copy and paste.    

To show that the rtl510 is a ANT + device here ya go.

Physical Specifications

• Dimensions: 3.9” x 0.8” x 1.6" (98.6 x 19.7 x 39.6 mm)
• Weight: 2.5 oz (71.0 g)
• Modes: solid, night flash, day flash
• Lumens: 20 solid, 29 night flash, 65 day flash
• Battery life: 6 hours solid, 6 hours night flash, 15 hours day flash
• ANT+®: Yes
• Water rating: IPX7
  • Viewing angle: 220°
    
    
    To say that it was clear that it does not support cellphones????? SO WHAT? Things are upgradeable.  We should be pushing companies to increase product longevity and keep things out of land fills.....  
    
    If other companies like wahoo can add the rtl510 radar to their computers then for sure it could be done for a cell phone by garmin.
    
    Whats next...... The documentation on your bike clearly shows that it is not to be ridden in anything but perfect sunny weather during the hours of 10:00 and 15:00 with a low relative humidity and on roads that vehicles and pedestrians do not have access to???

                        At any point that your bike get close to a four legged animal or a glass of milk your warranty immediately becomes null and void. 
Thanks for your purchase..

Just went through the documentation and I do not see cell phones listed anywhere. I am usually wrong though.