I am sharing my location with some friends using Apple's Find My Friend service.
I am curious to know if they get to know how many times and when I have looked them up using Find My Friend?
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As per @ Nimesh Neema answer https://apple.stackexchange.com/a/339887/46541
Your location is sent from your device only when someone requests to see it.
It means, if you request your friends location, your phone knows his number (you shared it) and will send a "Ping signal" to find it.
Once your friends phone receives the Ping request it will reply to you with the location data.
So theoretically YES, your friend could know you looked him up (Ping), if he has the tools and knowhow.
Some more technical stuff about it.. Officially, in an IP network, a ping is a network took that allows you to determine if a host is available on the network or not. It uses ICMP echo packets (https://tools.ietf.org/html/rfc792) to do the deed. When somebody says ping a mobile on the network, what he really implies is to determine if where (what cell it is connected to) that mobile is in the network. So, this can mean the mobile is trigger to do a forced location update (LU). The mobile then reports itself into the network with its latest information.
When sharing location with friends using Find My Friends, the other person doesn’t know how many times their friends have looked them up. They don't get any notification or there isn't any log of lookup incidents made available to them.
The location is sent from the friends device only when you request to see it. The location isn't transmitted on a regular interval.
For more information on setting up and using Find My Friends, it is advised to go through the Apple support article, Set up and use Find My Friends.
Do note that your friend(s) can choose to stop sharing their location at any time and can also choose to share their location using the device of their choice (e.g. if they are also using an iPad along with an iPhone and signed-into it using the same Apple ID, they may choose to share their location via the iPad. This may differ from their current physical location).
A couple more important points to note from the article:
You can follow up to 100 friends.
Your location is sent from your device only when someone requests to see it. Your location isn't transmitted on a regular interval.