Madam Rohayah Arshad, 55, heard three loud bangs outside her flat in Yishun on Sunday night.
Her neighbour, Madam Hariani Hashim, 44, saw smoke from her kitchen window and smelled burning plastic.
When Madam Rohayah called her, she told her to get out of her flat.
In her haste to leave, Madam Rohayah, who has difficulty walking, left her walking stick at home.
One fire engine and two fire bikes were sent to the block, but there was no fire. Investigations are ongoing.