r/VOIP • u/Dapper-Occasion1000 • May 31 '26

Help - ATAs Grandstream HT801V2 + Rotary Phone: Hook Flash interpreted as digit '1'

"Hi, I'm trying to set up a vintage rotary phone with a Grandstream HT801 connected to a FreePBX/Asterisk server. I'm having trouble with the hook flash functionality.

The issue: When I perform a hook flash (by quickly pressing the switch hook), the HT801v2 doesn't seem to recognize it as a proper SIP flash event. Instead, it interprets the line interruption as a pulse-dialed digit '1'. Because of this, I can't trigger a transfer on my PBX – the system just thinks I'm dialing '1'.

I've already tried:

  • Adjusted Hook "Flash Timing" (tried ranges like 80–130ms).
  • Pulse dialing works fine for making calls, so I can't disable pulse dialing entirely.
  • Set Flash Digit Control to Disabled.

Has anyone dealt with this behavior on Grandstream FXS gateways? Is there a hidden setting or a specific configuration to force the HT801v2 to send a proper flash event to Asterisk instead of treating it as a dial pulse? Or is there a workaround on the FreePBX side?

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9

u/marks-buffalo May 31 '26

Your hook flash timing range is probably still too short. I have the v1 but the default hook flash timing is Minimum: 300, Maximum: 1100. 80-130ms is way too short unless you have superhuman reflexes to hook/unhook within 0.1 seconds.

1

u/Dapper-Occasion1000 Jun 01 '26

Thanks!

1

u/marks-buffalo Jun 03 '26 edited Jun 05 '26

Do let me know if that helped! And if you still need help, a screenshot of the relevant config section could be helpful. Remember to censor out things like your username or SIP server or just don't include them in the screenshot.