Cover Page - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2020	Feb. 18, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-37461
Entity Registrant Name	ALARM.COM HOLDINGS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-4247032
Entity Address, Address Line One	8281 Greensboro Drive
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Tysons
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	22102
City Area Code	877
Local Phone Number	389-4033
Title of 12(b) Security	Common Stock, $0.01 par value per share
Trading Symbol	ALRM
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 2.3
Entity Common Stock, Shares Outstanding (in shares)		49,586,789
Documents Incorporated by Reference	Portions of the registrant’s proxy statement to be filed with the Securities and Exchange Commission pursuant to Regulation 14A in connection with the registrant’s 2021 Annual Meeting of Stockholders, which will be filed subsequent to the date hereof, are incorporated by reference into Part III of this Form 10-K. Such proxy statement will be filed with the Securities and Exchange Commission not later than 120 days following the end of the registrant’s fiscal year ended December 31, 2020.
Entity Central Index Key	0001459200
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false