Dial tone is normally only applied to a line after a loop is applied to it**. For loop start lines, at least, applying a loop will answer any incoming call. For ground start lines, a loop isn’t applied until the ground start handshake has confirmed that dial tone would not be presented.
I’d also have to ask what your, unusual, underlying requirement is, because normal users simply don’t care about dial tone detection.
A final point is that, for anything sophisticated, you should be using ISDN, not analogue, as it is impossible for Asterisk to detect many supervision events on analogue lines reliably; they are only really suitable for human users.
A final question is what about our underlying requirement requires the use of ARI, rather than the standard dialplan applications?
If you are trying to minimize glare, the answer is to use ground start lines, not to listen for dial tone. The only reason to listen for dialtone would be to delay before dialing to ensure that the exchange had allocated the resources needed to originate the call.
** On Strowger it would only be applied when a first selector had been successfully seized. On systems with more centralized control, it would only be applied after a free register had been allocated.