How can I know if the other party's mobile phone is turned on without calling?

If it is not turned on, wait for him to turn on and receive the message, and the message will come back and say that it has been sent successfully. If the other party has not turned on the phone for more than 24 hours, there will be a message back to remind you that sending the message was unsuccessful, that is, it is no longer valid. The last message sent has expired. If you want the other party to inquire about his situation without knowing it, you can dial his number with another phone that is not yours. If it rings, you will hang up. He doesn't know your strange number, so he doesn't know who you are. If you prompt the other party to turn off the phone, it goes without saying. I'm not worried that he'll think you're checking to see if he has a crush on my boyfriend. I just used the transmitter to check if it was on. It's best to send it to him when he turns it off, because it means that he will receive your message as soon as he turns it on, which means that you will know when he turns it on. There is no other way but to install high-tech software in his mobile phone and know his location and mobile phone status anytime and anywhere. It's impossible ... (If you have so much money to buy this thing, you might as well hire a private detective)