Read a password: on mobile!
HTML + JavaScript, 20+105 = 125 bytes

&lt;input id=I oninput=v=I.value;s='*'.repeat(l=v.length-1);I.value=s+v[l];clearTimeout(I.t);I.t=setTimeout(`I.value=s+'*'`,1e3)


The delay between the entry of k and the letter becoming * is one second.

JavaScript oninput, Formatted

v=I.value;
s='*'.repeat(l=v.length-1);
I.value=s+v[l];
clearTimeout(I.t);
I.t=setTimeout(`I.value=s+'*'`,1e3)


Test Snippet

Added the ending bracket (&gt;) for better compatibility.



&lt;input id=I oninput=v=I.value;s='*'.repeat(l=v.length-1);I.value=s+v[l];clearTimeout(I.t);I.t=setTimeout(`I.value=s+'*'`,1e3)&gt;