How can I put that code in one line?

Try:
<%= check_box_tag "send_email", @repair_ticket.send_email,
@repair_ticket.send_email, {:disabled => true } %>

If @repair_ticket.send_email was set as a boolean value in a
migration, ROR should interpret the send_email field as true or false
and thus correctly check/uncheck the checkbox.

-Chris

Try:
<%= check_box_tag "send_email", @repair_ticket.send_email,
@repair_ticket.send_email, {:disabled => true } %>

If @repair_ticket.send_email was set as a boolean value in a
migration, ROR should interpret the send_email field as true or false
and thus correctly check/uncheck the checkbox.

or even

<%= check_box 'repair_ticket', 'send_email', :disabled => true %>
(but that will result in a different parameter name)

Fred